Merge tag 'locking-core-2023-05-05' of git://git.kernel.org/pub/scm/linux/kernel...

[linux-block.git] / fs / locks.c

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/locks.c
 *
 * We implement four types of file locks: BSD locks, posix locks, open
 * file description locks, and leases.  For details about BSD locks,
 * see the flock(2) man page; for details about the other three, see
 * fcntl(2).
 *
 *
 * Locking conflicts and dependencies:
 * If multiple threads attempt to lock the same byte (or flock the same file)
 * only one can be granted the lock, and other must wait their turn.
 * The first lock has been "applied" or "granted", the others are "waiting"
 * and are "blocked" by the "applied" lock..
 *
 * Waiting and applied locks are all kept in trees whose properties are:
 *
 *      - the root of a tree may be an applied or waiting lock.
 *      - every other node in the tree is a waiting lock that
 *        conflicts with every ancestor of that node.
 *
 * Every such tree begins life as a waiting singleton which obviously
 * satisfies the above properties.
 *
 * The only ways we modify trees preserve these properties:
 *
 *      1. We may add a new leaf node, but only after first verifying that it
 *         conflicts with all of its ancestors.
 *      2. We may remove the root of a tree, creating a new singleton
 *         tree from the root and N new trees rooted in the immediate
 *         children.
 *      3. If the root of a tree is not currently an applied lock, we may
 *         apply it (if possible).
 *      4. We may upgrade the root of the tree (either extend its range,
 *         or upgrade its entire range from read to write).
 *
 * When an applied lock is modified in a way that reduces or downgrades any
 * part of its range, we remove all its children (2 above).  This particularly
 * happens when a lock is unlocked.
 *
 * For each of those child trees we "wake up" the thread which is
 * waiting for the lock so it can continue handling as follows: if the
 * root of the tree applies, we do so (3).  If it doesn't, it must
 * conflict with some applied lock.  We remove (wake up) all of its children
 * (2), and add it is a new leaf to the tree rooted in the applied
 * lock (1).  We then repeat the process recursively with those
 * children.
 *
 */

#include <linux/capability.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/filelock.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/security.h>
#include <linux/slab.h>
#include <linux/syscalls.h>
#include <linux/time.h>
#include <linux/rcupdate.h>
#include <linux/pid_namespace.h>
#include <linux/hashtable.h>
#include <linux/percpu.h>
#include <linux/sysctl.h>

#define CREATE_TRACE_POINTS
#include <trace/events/filelock.h>

#include <linux/uaccess.h>

#define IS_POSIX(fl)    (fl->fl_flags & FL_POSIX)
#define IS_FLOCK(fl)    (fl->fl_flags & FL_FLOCK)
#define IS_LEASE(fl)    (fl->fl_flags & (FL_LEASE|FL_DELEG|FL_LAYOUT))
#define IS_OFDLCK(fl)   (fl->fl_flags & FL_OFDLCK)
#define IS_REMOTELCK(fl)        (fl->fl_pid <= 0)

static bool lease_breaking(struct file_lock *fl)
{
        return fl->fl_flags & (FL_UNLOCK_PENDING | FL_DOWNGRADE_PENDING);
}

static int target_leasetype(struct file_lock *fl)
{
        if (fl->fl_flags & FL_UNLOCK_PENDING)
                return F_UNLCK;
        if (fl->fl_flags & FL_DOWNGRADE_PENDING)
                return F_RDLCK;
        return fl->fl_type;
}

static int leases_enable = 1;
static int lease_break_time = 45;

#ifdef CONFIG_SYSCTL
static struct ctl_table locks_sysctls[] = {
        {
                .procname       = "leases-enable",
                .data           = &leases_enable,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
#ifdef CONFIG_MMU
        {
                .procname       = "lease-break-time",
                .data           = &lease_break_time,
                .maxlen         = sizeof(int),
                .mode           = 0644,
                .proc_handler   = proc_dointvec,
        },
#endif /* CONFIG_MMU */
        {}
};

static int __init init_fs_locks_sysctls(void)
{
        register_sysctl_init("fs", locks_sysctls);
        return 0;
}
early_initcall(init_fs_locks_sysctls);
#endif /* CONFIG_SYSCTL */

/*
 * The global file_lock_list is only used for displaying /proc/locks, so we
 * keep a list on each CPU, with each list protected by its own spinlock.
 * Global serialization is done using file_rwsem.
 *
 * Note that alterations to the list also require that the relevant flc_lock is
 * held.
 */
struct file_lock_list_struct {
        spinlock_t              lock;
        struct hlist_head       hlist;
};
static DEFINE_PER_CPU(struct file_lock_list_struct, file_lock_list);
DEFINE_STATIC_PERCPU_RWSEM(file_rwsem);


/*
 * The blocked_hash is used to find POSIX lock loops for deadlock detection.
 * It is protected by blocked_lock_lock.
 *
 * We hash locks by lockowner in order to optimize searching for the lock a
 * particular lockowner is waiting on.
 *
 * FIXME: make this value scale via some heuristic? We generally will want more
 * buckets when we have more lockowners holding locks, but that's a little
 * difficult to determine without knowing what the workload will look like.
 */
#define BLOCKED_HASH_BITS       7
static DEFINE_HASHTABLE(blocked_hash, BLOCKED_HASH_BITS);

/*
 * This lock protects the blocked_hash. Generally, if you're accessing it, you
 * want to be holding this lock.
 *
 * In addition, it also protects the fl->fl_blocked_requests list, and the
 * fl->fl_blocker pointer for file_lock structures that are acting as lock
 * requests (in contrast to those that are acting as records of acquired locks).
 *
 * Note that when we acquire this lock in order to change the above fields,
 * we often hold the flc_lock as well. In certain cases, when reading the fields
 * protected by this lock, we can skip acquiring it iff we already hold the
 * flc_lock.
 */
static DEFINE_SPINLOCK(blocked_lock_lock);

static struct kmem_cache *flctx_cache __read_mostly;
static struct kmem_cache *filelock_cache __read_mostly;

static struct file_lock_context *
locks_get_lock_context(struct inode *inode, int type)
{
        struct file_lock_context *ctx;

        /* paired with cmpxchg() below */
        ctx = locks_inode_context(inode);
        if (likely(ctx) || type == F_UNLCK)
                goto out;

        ctx = kmem_cache_alloc(flctx_cache, GFP_KERNEL);
        if (!ctx)
                goto out;

        spin_lock_init(&ctx->flc_lock);
        INIT_LIST_HEAD(&ctx->flc_flock);
        INIT_LIST_HEAD(&ctx->flc_posix);
        INIT_LIST_HEAD(&ctx->flc_lease);

        /*
         * Assign the pointer if it's not already assigned. If it is, then
         * free the context we just allocated.
         */
        if (cmpxchg(&inode->i_flctx, NULL, ctx)) {
                kmem_cache_free(flctx_cache, ctx);
                ctx = locks_inode_context(inode);
        }
out:
        trace_locks_get_lock_context(inode, type, ctx);
        return ctx;
}

static void
locks_dump_ctx_list(struct list_head *list, char *list_type)
{
        struct file_lock *fl;

        list_for_each_entry(fl, list, fl_list) {
                pr_warn("%s: fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u\n", list_type, fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
        }
}

static void
locks_check_ctx_lists(struct inode *inode)
{
        struct file_lock_context *ctx = inode->i_flctx;

        if (unlikely(!list_empty(&ctx->flc_flock) ||
                     !list_empty(&ctx->flc_posix) ||
                     !list_empty(&ctx->flc_lease))) {
                pr_warn("Leaked locks on dev=0x%x:0x%x ino=0x%lx:\n",
                        MAJOR(inode->i_sb->s_dev), MINOR(inode->i_sb->s_dev),
                        inode->i_ino);
                locks_dump_ctx_list(&ctx->flc_flock, "FLOCK");
                locks_dump_ctx_list(&ctx->flc_posix, "POSIX");
                locks_dump_ctx_list(&ctx->flc_lease, "LEASE");
        }
}

static void
locks_check_ctx_file_list(struct file *filp, struct list_head *list,
                                char *list_type)
{
        struct file_lock *fl;
        struct inode *inode = file_inode(filp);

        list_for_each_entry(fl, list, fl_list)
                if (fl->fl_file == filp)
                        pr_warn("Leaked %s lock on dev=0x%x:0x%x ino=0x%lx "
                                " fl_owner=%p fl_flags=0x%x fl_type=0x%x fl_pid=%u\n",
                                list_type, MAJOR(inode->i_sb->s_dev),
                                MINOR(inode->i_sb->s_dev), inode->i_ino,
                                fl->fl_owner, fl->fl_flags, fl->fl_type, fl->fl_pid);
}

void
locks_free_lock_context(struct inode *inode)
{
        struct file_lock_context *ctx = locks_inode_context(inode);

        if (unlikely(ctx)) {
                locks_check_ctx_lists(inode);
                kmem_cache_free(flctx_cache, ctx);
        }
}

static void locks_init_lock_heads(struct file_lock *fl)
{
        INIT_HLIST_NODE(&fl->fl_link);
        INIT_LIST_HEAD(&fl->fl_list);
        INIT_LIST_HEAD(&fl->fl_blocked_requests);
        INIT_LIST_HEAD(&fl->fl_blocked_member);
        init_waitqueue_head(&fl->fl_wait);
}

/* Allocate an empty lock structure. */
struct file_lock *locks_alloc_lock(void)
{
        struct file_lock *fl = kmem_cache_zalloc(filelock_cache, GFP_KERNEL);

        if (fl)
                locks_init_lock_heads(fl);

        return fl;
}
EXPORT_SYMBOL_GPL(locks_alloc_lock);

void locks_release_private(struct file_lock *fl)
{
        BUG_ON(waitqueue_active(&fl->fl_wait));
        BUG_ON(!list_empty(&fl->fl_list));
        BUG_ON(!list_empty(&fl->fl_blocked_requests));
        BUG_ON(!list_empty(&fl->fl_blocked_member));
        BUG_ON(!hlist_unhashed(&fl->fl_link));

        if (fl->fl_ops) {
                if (fl->fl_ops->fl_release_private)
                        fl->fl_ops->fl_release_private(fl);
                fl->fl_ops = NULL;
        }

        if (fl->fl_lmops) {
                if (fl->fl_lmops->lm_put_owner) {
                        fl->fl_lmops->lm_put_owner(fl->fl_owner);
                        fl->fl_owner = NULL;
                }
                fl->fl_lmops = NULL;
        }
}
EXPORT_SYMBOL_GPL(locks_release_private);

/**
 * locks_owner_has_blockers - Check for blocking lock requests
 * @flctx: file lock context
 * @owner: lock owner
 *
 * Return values:
 *   %true: @owner has at least one blocker
 *   %false: @owner has no blockers
 */
bool locks_owner_has_blockers(struct file_lock_context *flctx,
                fl_owner_t owner)
{
        struct file_lock *fl;

        spin_lock(&flctx->flc_lock);
        list_for_each_entry(fl, &flctx->flc_posix, fl_list) {
                if (fl->fl_owner != owner)
                        continue;
                if (!list_empty(&fl->fl_blocked_requests)) {
                        spin_unlock(&flctx->flc_lock);
                        return true;
                }
        }
        spin_unlock(&flctx->flc_lock);
        return false;
}
EXPORT_SYMBOL_GPL(locks_owner_has_blockers);

/* Free a lock which is not in use. */
void locks_free_lock(struct file_lock *fl)
{
        locks_release_private(fl);
        kmem_cache_free(filelock_cache, fl);
}
EXPORT_SYMBOL(locks_free_lock);

static void
locks_dispose_list(struct list_head *dispose)
{
        struct file_lock *fl;

        while (!list_empty(dispose)) {
                fl = list_first_entry(dispose, struct file_lock, fl_list);
                list_del_init(&fl->fl_list);
                locks_free_lock(fl);
        }
}

void locks_init_lock(struct file_lock *fl)
{
        memset(fl, 0, sizeof(struct file_lock));
        locks_init_lock_heads(fl);
}
EXPORT_SYMBOL(locks_init_lock);

/*
 * Initialize a new lock from an existing file_lock structure.
 */
void locks_copy_conflock(struct file_lock *new, struct file_lock *fl)
{
        new->fl_owner = fl->fl_owner;
        new->fl_pid = fl->fl_pid;
        new->fl_file = NULL;
        new->fl_flags = fl->fl_flags;
        new->fl_type = fl->fl_type;
        new->fl_start = fl->fl_start;
        new->fl_end = fl->fl_end;
        new->fl_lmops = fl->fl_lmops;
        new->fl_ops = NULL;

        if (fl->fl_lmops) {
                if (fl->fl_lmops->lm_get_owner)
                        fl->fl_lmops->lm_get_owner(fl->fl_owner);
        }
}
EXPORT_SYMBOL(locks_copy_conflock);

void locks_copy_lock(struct file_lock *new, struct file_lock *fl)
{
        /* "new" must be a freshly-initialized lock */
        WARN_ON_ONCE(new->fl_ops);

        locks_copy_conflock(new, fl);

        new->fl_file = fl->fl_file;
        new->fl_ops = fl->fl_ops;

        if (fl->fl_ops) {
                if (fl->fl_ops->fl_copy_lock)
                        fl->fl_ops->fl_copy_lock(new, fl);
        }
}
EXPORT_SYMBOL(locks_copy_lock);

static void locks_move_blocks(struct file_lock *new, struct file_lock *fl)
{
        struct file_lock *f;

        /*
         * As ctx->flc_lock is held, new requests cannot be added to
         * ->fl_blocked_requests, so we don't need a lock to check if it
         * is empty.
         */
        if (list_empty(&fl->fl_blocked_requests))
                return;
        spin_lock(&blocked_lock_lock);
        list_splice_init(&fl->fl_blocked_requests, &new->fl_blocked_requests);
        list_for_each_entry(f, &new->fl_blocked_requests, fl_blocked_member)
                f->fl_blocker = new;
        spin_unlock(&blocked_lock_lock);
}

static inline int flock_translate_cmd(int cmd) {
        switch (cmd) {
        case LOCK_SH:
                return F_RDLCK;
        case LOCK_EX:
                return F_WRLCK;
        case LOCK_UN:
                return F_UNLCK;
        }
        return -EINVAL;
}

/* Fill in a file_lock structure with an appropriate FLOCK lock. */
static void flock_make_lock(struct file *filp, struct file_lock *fl, int type)
{
        locks_init_lock(fl);

        fl->fl_file = filp;
        fl->fl_owner = filp;
        fl->fl_pid = current->tgid;
        fl->fl_flags = FL_FLOCK;
        fl->fl_type = type;
        fl->fl_end = OFFSET_MAX;
}

static int assign_type(struct file_lock *fl, long type)
{
        switch (type) {
        case F_RDLCK:
        case F_WRLCK:
        case F_UNLCK:
                fl->fl_type = type;
                break;
        default:
                return -EINVAL;
        }
        return 0;
}

static int flock64_to_posix_lock(struct file *filp, struct file_lock *fl,
                                 struct flock64 *l)
{
        switch (l->l_whence) {
        case SEEK_SET:
                fl->fl_start = 0;
                break;
        case SEEK_CUR:
                fl->fl_start = filp->f_pos;
                break;
        case SEEK_END:
                fl->fl_start = i_size_read(file_inode(filp));
                break;
        default:
                return -EINVAL;
        }
        if (l->l_start > OFFSET_MAX - fl->fl_start)
                return -EOVERFLOW;
        fl->fl_start += l->l_start;
        if (fl->fl_start < 0)
                return -EINVAL;

        /* POSIX-1996 leaves the case l->l_len < 0 undefined;
           POSIX-2001 defines it. */
        if (l->l_len > 0) {
                if (l->l_len - 1 > OFFSET_MAX - fl->fl_start)
                        return -EOVERFLOW;
                fl->fl_end = fl->fl_start + (l->l_len - 1);

        } else if (l->l_len < 0) {
                if (fl->fl_start + l->l_len < 0)
                        return -EINVAL;
                fl->fl_end = fl->fl_start - 1;
                fl->fl_start += l->l_len;
        } else
                fl->fl_end = OFFSET_MAX;

        fl->fl_owner = current->files;
        fl->fl_pid = current->tgid;
        fl->fl_file = filp;
        fl->fl_flags = FL_POSIX;
        fl->fl_ops = NULL;
        fl->fl_lmops = NULL;

        return assign_type(fl, l->l_type);
}

/* Verify a "struct flock" and copy it to a "struct file_lock" as a POSIX
 * style lock.
 */
static int flock_to_posix_lock(struct file *filp, struct file_lock *fl,
                               struct flock *l)
{
        struct flock64 ll = {
                .l_type = l->l_type,
                .l_whence = l->l_whence,
                .l_start = l->l_start,
                .l_len = l->l_len,
        };

        return flock64_to_posix_lock(filp, fl, &ll);
}

/* default lease lock manager operations */
static bool
lease_break_callback(struct file_lock *fl)
{
        kill_fasync(&fl->fl_fasync, SIGIO, POLL_MSG);
        return false;
}

static void
lease_setup(struct file_lock *fl, void **priv)
{
        struct file *filp = fl->fl_file;
        struct fasync_struct *fa = *priv;

        /*
         * fasync_insert_entry() returns the old entry if any. If there was no
         * old entry, then it used "priv" and inserted it into the fasync list.
         * Clear the pointer to indicate that it shouldn't be freed.
         */
        if (!fasync_insert_entry(fa->fa_fd, filp, &fl->fl_fasync, fa))
                *priv = NULL;

        __f_setown(filp, task_pid(current), PIDTYPE_TGID, 0);
}

static const struct lock_manager_operations lease_manager_ops = {
        .lm_break = lease_break_callback,
        .lm_change = lease_modify,
        .lm_setup = lease_setup,
};

/*
 * Initialize a lease, use the default lock manager operations
 */
static int lease_init(struct file *filp, long type, struct file_lock *fl)
{
        if (assign_type(fl, type) != 0)
                return -EINVAL;

        fl->fl_owner = filp;
        fl->fl_pid = current->tgid;

        fl->fl_file = filp;
        fl->fl_flags = FL_LEASE;
        fl->fl_start = 0;
        fl->fl_end = OFFSET_MAX;
        fl->fl_ops = NULL;
        fl->fl_lmops = &lease_manager_ops;
        return 0;
}

/* Allocate a file_lock initialised to this type of lease */
static struct file_lock *lease_alloc(struct file *filp, long type)
{
        struct file_lock *fl = locks_alloc_lock();
        int error = -ENOMEM;

        if (fl == NULL)
                return ERR_PTR(error);

        error = lease_init(filp, type, fl);
        if (error) {
                locks_free_lock(fl);
                return ERR_PTR(error);
        }
        return fl;
}

/* Check if two locks overlap each other.
 */
static inline int locks_overlap(struct file_lock *fl1, struct file_lock *fl2)
{
        return ((fl1->fl_end >= fl2->fl_start) &&
                (fl2->fl_end >= fl1->fl_start));
}

/*
 * Check whether two locks have the same owner.
 */
static int posix_same_owner(struct file_lock *fl1, struct file_lock *fl2)
{
        return fl1->fl_owner == fl2->fl_owner;
}

/* Must be called with the flc_lock held! */
static void locks_insert_global_locks(struct file_lock *fl)
{
        struct file_lock_list_struct *fll = this_cpu_ptr(&file_lock_list);

        percpu_rwsem_assert_held(&file_rwsem);

        spin_lock(&fll->lock);
        fl->fl_link_cpu = smp_processor_id();
        hlist_add_head(&fl->fl_link, &fll->hlist);
        spin_unlock(&fll->lock);
}

/* Must be called with the flc_lock held! */
static void locks_delete_global_locks(struct file_lock *fl)
{
        struct file_lock_list_struct *fll;

        percpu_rwsem_assert_held(&file_rwsem);

        /*
         * Avoid taking lock if already unhashed. This is safe since this check
         * is done while holding the flc_lock, and new insertions into the list
         * also require that it be held.
         */
        if (hlist_unhashed(&fl->fl_link))
                return;

        fll = per_cpu_ptr(&file_lock_list, fl->fl_link_cpu);
        spin_lock(&fll->lock);
        hlist_del_init(&fl->fl_link);
        spin_unlock(&fll->lock);
}

static unsigned long
posix_owner_key(struct file_lock *fl)
{
        return (unsigned long)fl->fl_owner;
}

static void locks_insert_global_blocked(struct file_lock *waiter)
{
        lockdep_assert_held(&blocked_lock_lock);

        hash_add(blocked_hash, &waiter->fl_link, posix_owner_key(waiter));
}

static void locks_delete_global_blocked(struct file_lock *waiter)
{
        lockdep_assert_held(&blocked_lock_lock);

        hash_del(&waiter->fl_link);
}

/* Remove waiter from blocker's block list.
 * When blocker ends up pointing to itself then the list is empty.
 *
 * Must be called with blocked_lock_lock held.
 */
static void __locks_delete_block(struct file_lock *waiter)
{
        locks_delete_global_blocked(waiter);
        list_del_init(&waiter->fl_blocked_member);
}

static void __locks_wake_up_blocks(struct file_lock *blocker)
{
        while (!list_empty(&blocker->fl_blocked_requests)) {
                struct file_lock *waiter;

                waiter = list_first_entry(&blocker->fl_blocked_requests,
                                          struct file_lock, fl_blocked_member);
                __locks_delete_block(waiter);
                if (waiter->fl_lmops && waiter->fl_lmops->lm_notify)
                        waiter->fl_lmops->lm_notify(waiter);
                else
                        wake_up(&waiter->fl_wait);

                /*
                 * The setting of fl_blocker to NULL marks the "done"
                 * point in deleting a block. Paired with acquire at the top
                 * of locks_delete_block().
                 */
                smp_store_release(&waiter->fl_blocker, NULL);
        }
}

/**
 *      locks_delete_block - stop waiting for a file lock
 *      @waiter: the lock which was waiting
 *
 *      lockd/nfsd need to disconnect the lock while working on it.
 */
int locks_delete_block(struct file_lock *waiter)
{
        int status = -ENOENT;

        /*
         * If fl_blocker is NULL, it won't be set again as this thread "owns"
         * the lock and is the only one that might try to claim the lock.
         *
         * We use acquire/release to manage fl_blocker so that we can
         * optimize away taking the blocked_lock_lock in many cases.
         *
         * The smp_load_acquire guarantees two things:
         *
         * 1/ that fl_blocked_requests can be tested locklessly. If something
         * was recently added to that list it must have been in a locked region
         * *before* the locked region when fl_blocker was set to NULL.
         *
         * 2/ that no other thread is accessing 'waiter', so it is safe to free
         * it.  __locks_wake_up_blocks is careful not to touch waiter after
         * fl_blocker is released.
         *
         * If a lockless check of fl_blocker shows it to be NULL, we know that
         * no new locks can be inserted into its fl_blocked_requests list, and
         * can avoid doing anything further if the list is empty.
         */
        if (!smp_load_acquire(&waiter->fl_blocker) &&
            list_empty(&waiter->fl_blocked_requests))
                return status;

        spin_lock(&blocked_lock_lock);
        if (waiter->fl_blocker)
                status = 0;
        __locks_wake_up_blocks(waiter);
        __locks_delete_block(waiter);

        /*
         * The setting of fl_blocker to NULL marks the "done" point in deleting
         * a block. Paired with acquire at the top of this function.
         */
        smp_store_release(&waiter->fl_blocker, NULL);
        spin_unlock(&blocked_lock_lock);
        return status;
}
EXPORT_SYMBOL(locks_delete_block);

/* Insert waiter into blocker's block list.
 * We use a circular list so that processes can be easily woken up in
 * the order they blocked. The documentation doesn't require this but
 * it seems like the reasonable thing to do.
 *
 * Must be called with both the flc_lock and blocked_lock_lock held. The
 * fl_blocked_requests list itself is protected by the blocked_lock_lock,
 * but by ensuring that the flc_lock is also held on insertions we can avoid
 * taking the blocked_lock_lock in some cases when we see that the
 * fl_blocked_requests list is empty.
 *
 * Rather than just adding to the list, we check for conflicts with any existing
 * waiters, and add beneath any waiter that blocks the new waiter.
 * Thus wakeups don't happen until needed.
 */
static void __locks_insert_block(struct file_lock *blocker,
                                 struct file_lock *waiter,
                                 bool conflict(struct file_lock *,
                                               struct file_lock *))
{
        struct file_lock *fl;
        BUG_ON(!list_empty(&waiter->fl_blocked_member));

new_blocker:
        list_for_each_entry(fl, &blocker->fl_blocked_requests, fl_blocked_member)
                if (conflict(fl, waiter)) {
                        blocker =  fl;
                        goto new_blocker;
                }
        waiter->fl_blocker = blocker;
        list_add_tail(&waiter->fl_blocked_member, &blocker->fl_blocked_requests);
        if (IS_POSIX(blocker) && !IS_OFDLCK(blocker))
                locks_insert_global_blocked(waiter);

        /* The requests in waiter->fl_blocked are known to conflict with
         * waiter, but might not conflict with blocker, or the requests
         * and lock which block it.  So they all need to be woken.
         */
        __locks_wake_up_blocks(waiter);
}

/* Must be called with flc_lock held. */
static void locks_insert_block(struct file_lock *blocker,
                               struct file_lock *waiter,
                               bool conflict(struct file_lock *,
                                             struct file_lock *))
{
        spin_lock(&blocked_lock_lock);
        __locks_insert_block(blocker, waiter, conflict);
        spin_unlock(&blocked_lock_lock);
}

/*
 * Wake up processes blocked waiting for blocker.
 *
 * Must be called with the inode->flc_lock held!
 */
static void locks_wake_up_blocks(struct file_lock *blocker)
{
        /*
         * Avoid taking global lock if list is empty. This is safe since new
         * blocked requests are only added to the list under the flc_lock, and
         * the flc_lock is always held here. Note that removal from the
         * fl_blocked_requests list does not require the flc_lock, so we must
         * recheck list_empty() after acquiring the blocked_lock_lock.
         */
        if (list_empty(&blocker->fl_blocked_requests))
                return;

        spin_lock(&blocked_lock_lock);
        __locks_wake_up_blocks(blocker);
        spin_unlock(&blocked_lock_lock);
}

static void
locks_insert_lock_ctx(struct file_lock *fl, struct list_head *before)
{
        list_add_tail(&fl->fl_list, before);
        locks_insert_global_locks(fl);
}

static void
locks_unlink_lock_ctx(struct file_lock *fl)
{
        locks_delete_global_locks(fl);
        list_del_init(&fl->fl_list);
        locks_wake_up_blocks(fl);
}

static void
locks_delete_lock_ctx(struct file_lock *fl, struct list_head *dispose)
{
        locks_unlink_lock_ctx(fl);
        if (dispose)
                list_add(&fl->fl_list, dispose);
        else
                locks_free_lock(fl);
}

/* Determine if lock sys_fl blocks lock caller_fl. Common functionality
 * checks for shared/exclusive status of overlapping locks.
 */
static bool locks_conflict(struct file_lock *caller_fl,
                           struct file_lock *sys_fl)
{
        if (sys_fl->fl_type == F_WRLCK)
                return true;
        if (caller_fl->fl_type == F_WRLCK)
                return true;
        return false;
}

/* Determine if lock sys_fl blocks lock caller_fl. POSIX specific
 * checking before calling the locks_conflict().
 */
static bool posix_locks_conflict(struct file_lock *caller_fl,
                                 struct file_lock *sys_fl)
{
        /* POSIX locks owned by the same process do not conflict with
         * each other.
         */
        if (posix_same_owner(caller_fl, sys_fl))
                return false;

        /* Check whether they overlap */
        if (!locks_overlap(caller_fl, sys_fl))
                return false;

        return locks_conflict(caller_fl, sys_fl);
}

/* Determine if lock sys_fl blocks lock caller_fl. FLOCK specific
 * checking before calling the locks_conflict().
 */
static bool flock_locks_conflict(struct file_lock *caller_fl,
                                 struct file_lock *sys_fl)
{
        /* FLOCK locks referring to the same filp do not conflict with
         * each other.
         */
        if (caller_fl->fl_file == sys_fl->fl_file)
                return false;

        return locks_conflict(caller_fl, sys_fl);
}

void
posix_test_lock(struct file *filp, struct file_lock *fl)
{
        struct file_lock *cfl;
        struct file_lock_context *ctx;
        struct inode *inode = file_inode(filp);
        void *owner;
        void (*func)(void);

        ctx = locks_inode_context(inode);
        if (!ctx || list_empty_careful(&ctx->flc_posix)) {
                fl->fl_type = F_UNLCK;
                return;
        }

retry:
        spin_lock(&ctx->flc_lock);
        list_for_each_entry(cfl, &ctx->flc_posix, fl_list) {
                if (!posix_locks_conflict(fl, cfl))
                        continue;
                if (cfl->fl_lmops && cfl->fl_lmops->lm_lock_expirable
                        && (*cfl->fl_lmops->lm_lock_expirable)(cfl)) {
                        owner = cfl->fl_lmops->lm_mod_owner;
                        func = cfl->fl_lmops->lm_expire_lock;
                        __module_get(owner);
                        spin_unlock(&ctx->flc_lock);
                        (*func)();
                        module_put(owner);
                        goto retry;
                }
                locks_copy_conflock(fl, cfl);
                goto out;
        }
        fl->fl_type = F_UNLCK;
out:
        spin_unlock(&ctx->flc_lock);
        return;
}
EXPORT_SYMBOL(posix_test_lock);

/*
 * Deadlock detection:
 *
 * We attempt to detect deadlocks that are due purely to posix file
 * locks.
 *
 * We assume that a task can be waiting for at most one lock at a time.
 * So for any acquired lock, the process holding that lock may be
 * waiting on at most one other lock.  That lock in turns may be held by
 * someone waiting for at most one other lock.  Given a requested lock
 * caller_fl which is about to wait for a conflicting lock block_fl, we
 * follow this chain of waiters to ensure we are not about to create a
 * cycle.
 *
 * Since we do this before we ever put a process to sleep on a lock, we
 * are ensured that there is never a cycle; that is what guarantees that
 * the while() loop in posix_locks_deadlock() eventually completes.
 *
 * Note: the above assumption may not be true when handling lock
 * requests from a broken NFS client. It may also fail in the presence
 * of tasks (such as posix threads) sharing the same open file table.
 * To handle those cases, we just bail out after a few iterations.
 *
 * For FL_OFDLCK locks, the owner is the filp, not the files_struct.
 * Because the owner is not even nominally tied to a thread of
 * execution, the deadlock detection below can't reasonably work well. Just
 * skip it for those.
 *
 * In principle, we could do a more limited deadlock detection on FL_OFDLCK
 * locks that just checks for the case where two tasks are attempting to
 * upgrade from read to write locks on the same inode.
 */

#define MAX_DEADLK_ITERATIONS 10

/* Find a lock that the owner of the given block_fl is blocking on. */
static struct file_lock *what_owner_is_waiting_for(struct file_lock *block_fl)
{
        struct file_lock *fl;

        hash_for_each_possible(blocked_hash, fl, fl_link, posix_owner_key(block_fl)) {
                if (posix_same_owner(fl, block_fl)) {
                        while (fl->fl_blocker)
                                fl = fl->fl_blocker;
                        return fl;
                }
        }
        return NULL;
}

/* Must be called with the blocked_lock_lock held! */
static int posix_locks_deadlock(struct file_lock *caller_fl,
                                struct file_lock *block_fl)
{
        int i = 0;

        lockdep_assert_held(&blocked_lock_lock);

        /*
         * This deadlock detector can't reasonably detect deadlocks with
         * FL_OFDLCK locks, since they aren't owned by a process, per-se.
         */
        if (IS_OFDLCK(caller_fl))
                return 0;

        while ((block_fl = what_owner_is_waiting_for(block_fl))) {
                if (i++ > MAX_DEADLK_ITERATIONS)
                        return 0;
                if (posix_same_owner(caller_fl, block_fl))
                        return 1;
        }
        return 0;
}

/* Try to create a FLOCK lock on filp. We always insert new FLOCK locks
 * after any leases, but before any posix locks.
 *
 * Note that if called with an FL_EXISTS argument, the caller may determine
 * whether or not a lock was successfully freed by testing the return
 * value for -ENOENT.
 */
static int flock_lock_inode(struct inode *inode, struct file_lock *request)
{
        struct file_lock *new_fl = NULL;
        struct file_lock *fl;
        struct file_lock_context *ctx;
        int error = 0;
        bool found = false;
        LIST_HEAD(dispose);

        ctx = locks_get_lock_context(inode, request->fl_type);
        if (!ctx) {
                if (request->fl_type != F_UNLCK)
                        return -ENOMEM;
                return (request->fl_flags & FL_EXISTS) ? -ENOENT : 0;
        }

        if (!(request->fl_flags & FL_ACCESS) && (request->fl_type != F_UNLCK)) {
                new_fl = locks_alloc_lock();
                if (!new_fl)
                        return -ENOMEM;
        }

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        if (request->fl_flags & FL_ACCESS)
                goto find_conflict;

        list_for_each_entry(fl, &ctx->flc_flock, fl_list) {
                if (request->fl_file != fl->fl_file)
                        continue;
                if (request->fl_type == fl->fl_type)
                        goto out;
                found = true;
                locks_delete_lock_ctx(fl, &dispose);
                break;
        }

        if (request->fl_type == F_UNLCK) {
                if ((request->fl_flags & FL_EXISTS) && !found)
                        error = -ENOENT;
                goto out;
        }

find_conflict:
        list_for_each_entry(fl, &ctx->flc_flock, fl_list) {
                if (!flock_locks_conflict(request, fl))
                        continue;
                error = -EAGAIN;
                if (!(request->fl_flags & FL_SLEEP))
                        goto out;
                error = FILE_LOCK_DEFERRED;
                locks_insert_block(fl, request, flock_locks_conflict);
                goto out;
        }
        if (request->fl_flags & FL_ACCESS)
                goto out;
        locks_copy_lock(new_fl, request);
        locks_move_blocks(new_fl, request);
        locks_insert_lock_ctx(new_fl, &ctx->flc_flock);
        new_fl = NULL;
        error = 0;

out:
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);
        if (new_fl)
                locks_free_lock(new_fl);
        locks_dispose_list(&dispose);
        trace_flock_lock_inode(inode, request, error);
        return error;
}

static int posix_lock_inode(struct inode *inode, struct file_lock *request,
                            struct file_lock *conflock)
{
        struct file_lock *fl, *tmp;
        struct file_lock *new_fl = NULL;
        struct file_lock *new_fl2 = NULL;
        struct file_lock *left = NULL;
        struct file_lock *right = NULL;
        struct file_lock_context *ctx;
        int error;
        bool added = false;
        LIST_HEAD(dispose);
        void *owner;
        void (*func)(void);

        ctx = locks_get_lock_context(inode, request->fl_type);
        if (!ctx)
                return (request->fl_type == F_UNLCK) ? 0 : -ENOMEM;

        /*
         * We may need two file_lock structures for this operation,
         * so we get them in advance to avoid races.
         *
         * In some cases we can be sure, that no new locks will be needed
         */
        if (!(request->fl_flags & FL_ACCESS) &&
            (request->fl_type != F_UNLCK ||
             request->fl_start != 0 || request->fl_end != OFFSET_MAX)) {
                new_fl = locks_alloc_lock();
                new_fl2 = locks_alloc_lock();
        }

retry:
        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        /*
         * New lock request. Walk all POSIX locks and look for conflicts. If
         * there are any, either return error or put the request on the
         * blocker's list of waiters and the global blocked_hash.
         */
        if (request->fl_type != F_UNLCK) {
                list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
                        if (!posix_locks_conflict(request, fl))
                                continue;
                        if (fl->fl_lmops && fl->fl_lmops->lm_lock_expirable
                                && (*fl->fl_lmops->lm_lock_expirable)(fl)) {
                                owner = fl->fl_lmops->lm_mod_owner;
                                func = fl->fl_lmops->lm_expire_lock;
                                __module_get(owner);
                                spin_unlock(&ctx->flc_lock);
                                percpu_up_read(&file_rwsem);
                                (*func)();
                                module_put(owner);
                                goto retry;
                        }
                        if (conflock)
                                locks_copy_conflock(conflock, fl);
                        error = -EAGAIN;
                        if (!(request->fl_flags & FL_SLEEP))
                                goto out;
                        /*
                         * Deadlock detection and insertion into the blocked
                         * locks list must be done while holding the same lock!
                         */
                        error = -EDEADLK;
                        spin_lock(&blocked_lock_lock);
                        /*
                         * Ensure that we don't find any locks blocked on this
                         * request during deadlock detection.
                         */
                        __locks_wake_up_blocks(request);
                        if (likely(!posix_locks_deadlock(request, fl))) {
                                error = FILE_LOCK_DEFERRED;
                                __locks_insert_block(fl, request,
                                                     posix_locks_conflict);
                        }
                        spin_unlock(&blocked_lock_lock);
                        goto out;
                }
        }

        /* If we're just looking for a conflict, we're done. */
        error = 0;
        if (request->fl_flags & FL_ACCESS)
                goto out;

        /* Find the first old lock with the same owner as the new lock */
        list_for_each_entry(fl, &ctx->flc_posix, fl_list) {
                if (posix_same_owner(request, fl))
                        break;
        }

        /* Process locks with this owner. */
        list_for_each_entry_safe_from(fl, tmp, &ctx->flc_posix, fl_list) {
                if (!posix_same_owner(request, fl))
                        break;

                /* Detect adjacent or overlapping regions (if same lock type) */
                if (request->fl_type == fl->fl_type) {
                        /* In all comparisons of start vs end, use
                         * "start - 1" rather than "end + 1". If end
                         * is OFFSET_MAX, end + 1 will become negative.
                         */
                        if (fl->fl_end < request->fl_start - 1)
                                continue;
                        /* If the next lock in the list has entirely bigger
                         * addresses than the new one, insert the lock here.
                         */
                        if (fl->fl_start - 1 > request->fl_end)
                                break;

                        /* If we come here, the new and old lock are of the
                         * same type and adjacent or overlapping. Make one
                         * lock yielding from the lower start address of both
                         * locks to the higher end address.
                         */
                        if (fl->fl_start > request->fl_start)
                                fl->fl_start = request->fl_start;
                        else
                                request->fl_start = fl->fl_start;
                        if (fl->fl_end < request->fl_end)
                                fl->fl_end = request->fl_end;
                        else
                                request->fl_end = fl->fl_end;
                        if (added) {
                                locks_delete_lock_ctx(fl, &dispose);
                                continue;
                        }
                        request = fl;
                        added = true;
                } else {
                        /* Processing for different lock types is a bit
                         * more complex.
                         */
                        if (fl->fl_end < request->fl_start)
                                continue;
                        if (fl->fl_start > request->fl_end)
                                break;
                        if (request->fl_type == F_UNLCK)
                                added = true;
                        if (fl->fl_start < request->fl_start)
                                left = fl;
                        /* If the next lock in the list has a higher end
                         * address than the new one, insert the new one here.
                         */
                        if (fl->fl_end > request->fl_end) {
                                right = fl;
                                break;
                        }
                        if (fl->fl_start >= request->fl_start) {
                                /* The new lock completely replaces an old
                                 * one (This may happen several times).
                                 */
                                if (added) {
                                        locks_delete_lock_ctx(fl, &dispose);
                                        continue;
                                }
                                /*
                                 * Replace the old lock with new_fl, and
                                 * remove the old one. It's safe to do the
                                 * insert here since we know that we won't be
                                 * using new_fl later, and that the lock is
                                 * just replacing an existing lock.
                                 */
                                error = -ENOLCK;
                                if (!new_fl)
                                        goto out;
                                locks_copy_lock(new_fl, request);
                                locks_move_blocks(new_fl, request);
                                request = new_fl;
                                new_fl = NULL;
                                locks_insert_lock_ctx(request, &fl->fl_list);
                                locks_delete_lock_ctx(fl, &dispose);
                                added = true;
                        }
                }
        }

        /*
         * The above code only modifies existing locks in case of merging or
         * replacing. If new lock(s) need to be inserted all modifications are
         * done below this, so it's safe yet to bail out.
         */
        error = -ENOLCK; /* "no luck" */
        if (right && left == right && !new_fl2)
                goto out;

        error = 0;
        if (!added) {
                if (request->fl_type == F_UNLCK) {
                        if (request->fl_flags & FL_EXISTS)
                                error = -ENOENT;
                        goto out;
                }

                if (!new_fl) {
                        error = -ENOLCK;
                        goto out;
                }
                locks_copy_lock(new_fl, request);
                locks_move_blocks(new_fl, request);
                locks_insert_lock_ctx(new_fl, &fl->fl_list);
                fl = new_fl;
                new_fl = NULL;
        }
        if (right) {
                if (left == right) {
                        /* The new lock breaks the old one in two pieces,
                         * so we have to use the second new lock.
                         */
                        left = new_fl2;
                        new_fl2 = NULL;
                        locks_copy_lock(left, right);
                        locks_insert_lock_ctx(left, &fl->fl_list);
                }
                right->fl_start = request->fl_end + 1;
                locks_wake_up_blocks(right);
        }
        if (left) {
                left->fl_end = request->fl_start - 1;
                locks_wake_up_blocks(left);
        }
 out:
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);
        /*
         * Free any unused locks.
         */
        if (new_fl)
                locks_free_lock(new_fl);
        if (new_fl2)
                locks_free_lock(new_fl2);
        locks_dispose_list(&dispose);
        trace_posix_lock_inode(inode, request, error);

        return error;
}

/**
 * posix_lock_file - Apply a POSIX-style lock to a file
 * @filp: The file to apply the lock to
 * @fl: The lock to be applied
 * @conflock: Place to return a copy of the conflicting lock, if found.
 *
 * Add a POSIX style lock to a file.
 * We merge adjacent & overlapping locks whenever possible.
 * POSIX locks are sorted by owner task, then by starting address
 *
 * Note that if called with an FL_EXISTS argument, the caller may determine
 * whether or not a lock was successfully freed by testing the return
 * value for -ENOENT.
 */
int posix_lock_file(struct file *filp, struct file_lock *fl,
                        struct file_lock *conflock)
{
        return posix_lock_inode(file_inode(filp), fl, conflock);
}
EXPORT_SYMBOL(posix_lock_file);

/**
 * posix_lock_inode_wait - Apply a POSIX-style lock to a file
 * @inode: inode of file to which lock request should be applied
 * @fl: The lock to be applied
 *
 * Apply a POSIX style lock request to an inode.
 */
static int posix_lock_inode_wait(struct inode *inode, struct file_lock *fl)
{
        int error;
        might_sleep ();
        for (;;) {
                error = posix_lock_inode(inode, fl, NULL);
                if (error != FILE_LOCK_DEFERRED)
                        break;
                error = wait_event_interruptible(fl->fl_wait,
                                        list_empty(&fl->fl_blocked_member));
                if (error)
                        break;
        }
        locks_delete_block(fl);
        return error;
}

static void lease_clear_pending(struct file_lock *fl, int arg)
{
        switch (arg) {
        case F_UNLCK:
                fl->fl_flags &= ~FL_UNLOCK_PENDING;
                fallthrough;
        case F_RDLCK:
                fl->fl_flags &= ~FL_DOWNGRADE_PENDING;
        }
}

/* We already had a lease on this file; just change its type */
int lease_modify(struct file_lock *fl, int arg, struct list_head *dispose)
{
        int error = assign_type(fl, arg);

        if (error)
                return error;
        lease_clear_pending(fl, arg);
        locks_wake_up_blocks(fl);
        if (arg == F_UNLCK) {
                struct file *filp = fl->fl_file;

                f_delown(filp);
                filp->f_owner.signum = 0;
                fasync_helper(0, fl->fl_file, 0, &fl->fl_fasync);
                if (fl->fl_fasync != NULL) {
                        printk(KERN_ERR "locks_delete_lock: fasync == %p\n", fl->fl_fasync);
                        fl->fl_fasync = NULL;
                }
                locks_delete_lock_ctx(fl, dispose);
        }
        return 0;
}
EXPORT_SYMBOL(lease_modify);

static bool past_time(unsigned long then)
{
        if (!then)
                /* 0 is a special value meaning "this never expires": */
                return false;
        return time_after(jiffies, then);
}

static void time_out_leases(struct inode *inode, struct list_head *dispose)
{
        struct file_lock_context *ctx = inode->i_flctx;
        struct file_lock *fl, *tmp;

        lockdep_assert_held(&ctx->flc_lock);

        list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {
                trace_time_out_leases(inode, fl);
                if (past_time(fl->fl_downgrade_time))
                        lease_modify(fl, F_RDLCK, dispose);
                if (past_time(fl->fl_break_time))
                        lease_modify(fl, F_UNLCK, dispose);
        }
}

static bool leases_conflict(struct file_lock *lease, struct file_lock *breaker)
{
        bool rc;

        if (lease->fl_lmops->lm_breaker_owns_lease
                        && lease->fl_lmops->lm_breaker_owns_lease(lease))
                return false;
        if ((breaker->fl_flags & FL_LAYOUT) != (lease->fl_flags & FL_LAYOUT)) {
                rc = false;
                goto trace;
        }
        if ((breaker->fl_flags & FL_DELEG) && (lease->fl_flags & FL_LEASE)) {
                rc = false;
                goto trace;
        }

        rc = locks_conflict(breaker, lease);
trace:
        trace_leases_conflict(rc, lease, breaker);
        return rc;
}

static bool
any_leases_conflict(struct inode *inode, struct file_lock *breaker)
{
        struct file_lock_context *ctx = inode->i_flctx;
        struct file_lock *fl;

        lockdep_assert_held(&ctx->flc_lock);

        list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
                if (leases_conflict(fl, breaker))
                        return true;
        }
        return false;
}

/**
 *      __break_lease   -       revoke all outstanding leases on file
 *      @inode: the inode of the file to return
 *      @mode: O_RDONLY: break only write leases; O_WRONLY or O_RDWR:
 *          break all leases
 *      @type: FL_LEASE: break leases and delegations; FL_DELEG: break
 *          only delegations
 *
 *      break_lease (inlined for speed) has checked there already is at least
 *      some kind of lock (maybe a lease) on this file.  Leases are broken on
 *      a call to open() or truncate().  This function can sleep unless you
 *      specified %O_NONBLOCK to your open().
 */
int __break_lease(struct inode *inode, unsigned int mode, unsigned int type)
{
        int error = 0;
        struct file_lock_context *ctx;
        struct file_lock *new_fl, *fl, *tmp;
        unsigned long break_time;
        int want_write = (mode & O_ACCMODE) != O_RDONLY;
        LIST_HEAD(dispose);

        new_fl = lease_alloc(NULL, want_write ? F_WRLCK : F_RDLCK);
        if (IS_ERR(new_fl))
                return PTR_ERR(new_fl);
        new_fl->fl_flags = type;

        /* typically we will check that ctx is non-NULL before calling */
        ctx = locks_inode_context(inode);
        if (!ctx) {
                WARN_ON_ONCE(1);
                goto free_lock;
        }

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);

        time_out_leases(inode, &dispose);

        if (!any_leases_conflict(inode, new_fl))
                goto out;

        break_time = 0;
        if (lease_break_time > 0) {
                break_time = jiffies + lease_break_time * HZ;
                if (break_time == 0)
                        break_time++;   /* so that 0 means no break time */
        }

        list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list) {
                if (!leases_conflict(fl, new_fl))
                        continue;
                if (want_write) {
                        if (fl->fl_flags & FL_UNLOCK_PENDING)
                                continue;
                        fl->fl_flags |= FL_UNLOCK_PENDING;
                        fl->fl_break_time = break_time;
                } else {
                        if (lease_breaking(fl))
                                continue;
                        fl->fl_flags |= FL_DOWNGRADE_PENDING;
                        fl->fl_downgrade_time = break_time;
                }
                if (fl->fl_lmops->lm_break(fl))
                        locks_delete_lock_ctx(fl, &dispose);
        }

        if (list_empty(&ctx->flc_lease))
                goto out;

        if (mode & O_NONBLOCK) {
                trace_break_lease_noblock(inode, new_fl);
                error = -EWOULDBLOCK;
                goto out;
        }

restart:
        fl = list_first_entry(&ctx->flc_lease, struct file_lock, fl_list);
        break_time = fl->fl_break_time;
        if (break_time != 0)
                break_time -= jiffies;
        if (break_time == 0)
                break_time++;
        locks_insert_block(fl, new_fl, leases_conflict);
        trace_break_lease_block(inode, new_fl);
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);

        locks_dispose_list(&dispose);
        error = wait_event_interruptible_timeout(new_fl->fl_wait,
                                        list_empty(&new_fl->fl_blocked_member),
                                        break_time);

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        trace_break_lease_unblock(inode, new_fl);
        locks_delete_block(new_fl);
        if (error >= 0) {
                /*
                 * Wait for the next conflicting lease that has not been
                 * broken yet
                 */
                if (error == 0)
                        time_out_leases(inode, &dispose);
                if (any_leases_conflict(inode, new_fl))
                        goto restart;
                error = 0;
        }
out:
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);
        locks_dispose_list(&dispose);
free_lock:
        locks_free_lock(new_fl);
        return error;
}
EXPORT_SYMBOL(__break_lease);

/**
 *      lease_get_mtime - update modified time of an inode with exclusive lease
 *      @inode: the inode
 *      @time:  pointer to a timespec which contains the last modified time
 *
 * This is to force NFS clients to flush their caches for files with
 * exclusive leases.  The justification is that if someone has an
 * exclusive lease, then they could be modifying it.
 */
void lease_get_mtime(struct inode *inode, struct timespec64 *time)
{
        bool has_lease = false;
        struct file_lock_context *ctx;
        struct file_lock *fl;

        ctx = locks_inode_context(inode);
        if (ctx && !list_empty_careful(&ctx->flc_lease)) {
                spin_lock(&ctx->flc_lock);
                fl = list_first_entry_or_null(&ctx->flc_lease,
                                              struct file_lock, fl_list);
                if (fl && (fl->fl_type == F_WRLCK))
                        has_lease = true;
                spin_unlock(&ctx->flc_lock);
        }

        if (has_lease)
                *time = current_time(inode);
}
EXPORT_SYMBOL(lease_get_mtime);

/**
 *      fcntl_getlease - Enquire what lease is currently active
 *      @filp: the file
 *
 *      The value returned by this function will be one of
 *      (if no lease break is pending):
 *
 *      %F_RDLCK to indicate a shared lease is held.
 *
 *      %F_WRLCK to indicate an exclusive lease is held.
 *
 *      %F_UNLCK to indicate no lease is held.
 *
 *      (if a lease break is pending):
 *
 *      %F_RDLCK to indicate an exclusive lease needs to be
 *              changed to a shared lease (or removed).
 *
 *      %F_UNLCK to indicate the lease needs to be removed.
 *
 *      XXX: sfr & willy disagree over whether F_INPROGRESS
 *      should be returned to userspace.
 */
int fcntl_getlease(struct file *filp)
{
        struct file_lock *fl;
        struct inode *inode = file_inode(filp);
        struct file_lock_context *ctx;
        int type = F_UNLCK;
        LIST_HEAD(dispose);

        ctx = locks_inode_context(inode);
        if (ctx && !list_empty_careful(&ctx->flc_lease)) {
                percpu_down_read(&file_rwsem);
                spin_lock(&ctx->flc_lock);
                time_out_leases(inode, &dispose);
                list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
                        if (fl->fl_file != filp)
                                continue;
                        type = target_leasetype(fl);
                        break;
                }
                spin_unlock(&ctx->flc_lock);
                percpu_up_read(&file_rwsem);

                locks_dispose_list(&dispose);
        }
        return type;
}

/**
 * check_conflicting_open - see if the given file points to an inode that has
 *                          an existing open that would conflict with the
 *                          desired lease.
 * @filp:       file to check
 * @arg:        type of lease that we're trying to acquire
 * @flags:      current lock flags
 *
 * Check to see if there's an existing open fd on this file that would
 * conflict with the lease we're trying to set.
 */
static int
check_conflicting_open(struct file *filp, const long arg, int flags)
{
        struct inode *inode = file_inode(filp);
        int self_wcount = 0, self_rcount = 0;

        if (flags & FL_LAYOUT)
                return 0;
        if (flags & FL_DELEG)
                /* We leave these checks to the caller */
                return 0;

        if (arg == F_RDLCK)
                return inode_is_open_for_write(inode) ? -EAGAIN : 0;
        else if (arg != F_WRLCK)
                return 0;

        /*
         * Make sure that only read/write count is from lease requestor.
         * Note that this will result in denying write leases when i_writecount
         * is negative, which is what we want.  (We shouldn't grant write leases
         * on files open for execution.)
         */
        if (filp->f_mode & FMODE_WRITE)
                self_wcount = 1;
        else if (filp->f_mode & FMODE_READ)
                self_rcount = 1;

        if (atomic_read(&inode->i_writecount) != self_wcount ||
            atomic_read(&inode->i_readcount) != self_rcount)
                return -EAGAIN;

        return 0;
}

static int
generic_add_lease(struct file *filp, long arg, struct file_lock **flp, void **priv)
{
        struct file_lock *fl, *my_fl = NULL, *lease;
        struct inode *inode = file_inode(filp);
        struct file_lock_context *ctx;
        bool is_deleg = (*flp)->fl_flags & FL_DELEG;
        int error;
        LIST_HEAD(dispose);

        lease = *flp;
        trace_generic_add_lease(inode, lease);

        /* Note that arg is never F_UNLCK here */
        ctx = locks_get_lock_context(inode, arg);
        if (!ctx)
                return -ENOMEM;

        /*
         * In the delegation case we need mutual exclusion with
         * a number of operations that take the i_mutex.  We trylock
         * because delegations are an optional optimization, and if
         * there's some chance of a conflict--we'd rather not
         * bother, maybe that's a sign this just isn't a good file to
         * hand out a delegation on.
         */
        if (is_deleg && !inode_trylock(inode))
                return -EAGAIN;

        if (is_deleg && arg == F_WRLCK) {
                /* Write delegations are not currently supported: */
                inode_unlock(inode);
                WARN_ON_ONCE(1);
                return -EINVAL;
        }

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        time_out_leases(inode, &dispose);
        error = check_conflicting_open(filp, arg, lease->fl_flags);
        if (error)
                goto out;

        /*
         * At this point, we know that if there is an exclusive
         * lease on this file, then we hold it on this filp
         * (otherwise our open of this file would have blocked).
         * And if we are trying to acquire an exclusive lease,
         * then the file is not open by anyone (including us)
         * except for this filp.
         */
        error = -EAGAIN;
        list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
                if (fl->fl_file == filp &&
                    fl->fl_owner == lease->fl_owner) {
                        my_fl = fl;
                        continue;
                }

                /*
                 * No exclusive leases if someone else has a lease on
                 * this file:
                 */
                if (arg == F_WRLCK)
                        goto out;
                /*
                 * Modifying our existing lease is OK, but no getting a
                 * new lease if someone else is opening for write:
                 */
                if (fl->fl_flags & FL_UNLOCK_PENDING)
                        goto out;
        }

        if (my_fl != NULL) {
                lease = my_fl;
                error = lease->fl_lmops->lm_change(lease, arg, &dispose);
                if (error)
                        goto out;
                goto out_setup;
        }

        error = -EINVAL;
        if (!leases_enable)
                goto out;

        locks_insert_lock_ctx(lease, &ctx->flc_lease);
        /*
         * The check in break_lease() is lockless. It's possible for another
         * open to race in after we did the earlier check for a conflicting
         * open but before the lease was inserted. Check again for a
         * conflicting open and cancel the lease if there is one.
         *
         * We also add a barrier here to ensure that the insertion of the lock
         * precedes these checks.
         */
        smp_mb();
        error = check_conflicting_open(filp, arg, lease->fl_flags);
        if (error) {
                locks_unlink_lock_ctx(lease);
                goto out;
        }

out_setup:
        if (lease->fl_lmops->lm_setup)
                lease->fl_lmops->lm_setup(lease, priv);
out:
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);
        locks_dispose_list(&dispose);
        if (is_deleg)
                inode_unlock(inode);
        if (!error && !my_fl)
                *flp = NULL;
        return error;
}

static int generic_delete_lease(struct file *filp, void *owner)
{
        int error = -EAGAIN;
        struct file_lock *fl, *victim = NULL;
        struct inode *inode = file_inode(filp);
        struct file_lock_context *ctx;
        LIST_HEAD(dispose);

        ctx = locks_inode_context(inode);
        if (!ctx) {
                trace_generic_delete_lease(inode, NULL);
                return error;
        }

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        list_for_each_entry(fl, &ctx->flc_lease, fl_list) {
                if (fl->fl_file == filp &&
                    fl->fl_owner == owner) {
                        victim = fl;
                        break;
                }
        }
        trace_generic_delete_lease(inode, victim);
        if (victim)
                error = fl->fl_lmops->lm_change(victim, F_UNLCK, &dispose);
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);
        locks_dispose_list(&dispose);
        return error;
}

/**
 *      generic_setlease        -       sets a lease on an open file
 *      @filp:  file pointer
 *      @arg:   type of lease to obtain
 *      @flp:   input - file_lock to use, output - file_lock inserted
 *      @priv:  private data for lm_setup (may be NULL if lm_setup
 *              doesn't require it)
 *
 *      The (input) flp->fl_lmops->lm_break function is required
 *      by break_lease().
 */
int generic_setlease(struct file *filp, long arg, struct file_lock **flp,
                        void **priv)
{
        struct inode *inode = file_inode(filp);
        vfsuid_t vfsuid = i_uid_into_vfsuid(file_mnt_idmap(filp), inode);
        int error;

        if ((!vfsuid_eq_kuid(vfsuid, current_fsuid())) && !capable(CAP_LEASE))
                return -EACCES;
        if (!S_ISREG(inode->i_mode))
                return -EINVAL;
        error = security_file_lock(filp, arg);
        if (error)
                return error;

        switch (arg) {
        case F_UNLCK:
                return generic_delete_lease(filp, *priv);
        case F_RDLCK:
        case F_WRLCK:
                if (!(*flp)->fl_lmops->lm_break) {
                        WARN_ON_ONCE(1);
                        return -ENOLCK;
                }

                return generic_add_lease(filp, arg, flp, priv);
        default:
                return -EINVAL;
        }
}
EXPORT_SYMBOL(generic_setlease);

/*
 * Kernel subsystems can register to be notified on any attempt to set
 * a new lease with the lease_notifier_chain. This is used by (e.g.) nfsd
 * to close files that it may have cached when there is an attempt to set a
 * conflicting lease.
 */
static struct srcu_notifier_head lease_notifier_chain;

static inline void
lease_notifier_chain_init(void)
{
        srcu_init_notifier_head(&lease_notifier_chain);
}

static inline void
setlease_notifier(long arg, struct file_lock *lease)
{
        if (arg != F_UNLCK)
                srcu_notifier_call_chain(&lease_notifier_chain, arg, lease);
}

int lease_register_notifier(struct notifier_block *nb)
{
        return srcu_notifier_chain_register(&lease_notifier_chain, nb);
}
EXPORT_SYMBOL_GPL(lease_register_notifier);

void lease_unregister_notifier(struct notifier_block *nb)
{
        srcu_notifier_chain_unregister(&lease_notifier_chain, nb);
}
EXPORT_SYMBOL_GPL(lease_unregister_notifier);

/**
 * vfs_setlease        -       sets a lease on an open file
 * @filp:       file pointer
 * @arg:        type of lease to obtain
 * @lease:      file_lock to use when adding a lease
 * @priv:       private info for lm_setup when adding a lease (may be
 *              NULL if lm_setup doesn't require it)
 *
 * Call this to establish a lease on the file. The "lease" argument is not
 * used for F_UNLCK requests and may be NULL. For commands that set or alter
 * an existing lease, the ``(*lease)->fl_lmops->lm_break`` operation must be
 * set; if not, this function will return -ENOLCK (and generate a scary-looking
 * stack trace).
 *
 * The "priv" pointer is passed directly to the lm_setup function as-is. It
 * may be NULL if the lm_setup operation doesn't require it.
 */
int
vfs_setlease(struct file *filp, long arg, struct file_lock **lease, void **priv)
{
        if (lease)
                setlease_notifier(arg, *lease);
        if (filp->f_op->setlease)
                return filp->f_op->setlease(filp, arg, lease, priv);
        else
                return generic_setlease(filp, arg, lease, priv);
}
EXPORT_SYMBOL_GPL(vfs_setlease);

static int do_fcntl_add_lease(unsigned int fd, struct file *filp, long arg)
{
        struct file_lock *fl;
        struct fasync_struct *new;
        int error;

        fl = lease_alloc(filp, arg);
        if (IS_ERR(fl))
                return PTR_ERR(fl);

        new = fasync_alloc();
        if (!new) {
                locks_free_lock(fl);
                return -ENOMEM;
        }
        new->fa_fd = fd;

        error = vfs_setlease(filp, arg, &fl, (void **)&new);
        if (fl)
                locks_free_lock(fl);
        if (new)
                fasync_free(new);
        return error;
}

/**
 *      fcntl_setlease  -       sets a lease on an open file
 *      @fd: open file descriptor
 *      @filp: file pointer
 *      @arg: type of lease to obtain
 *
 *      Call this fcntl to establish a lease on the file.
 *      Note that you also need to call %F_SETSIG to
 *      receive a signal when the lease is broken.
 */
int fcntl_setlease(unsigned int fd, struct file *filp, long arg)
{
        if (arg == F_UNLCK)
                return vfs_setlease(filp, F_UNLCK, NULL, (void **)&filp);
        return do_fcntl_add_lease(fd, filp, arg);
}

/**
 * flock_lock_inode_wait - Apply a FLOCK-style lock to a file
 * @inode: inode of the file to apply to
 * @fl: The lock to be applied
 *
 * Apply a FLOCK style lock request to an inode.
 */
static int flock_lock_inode_wait(struct inode *inode, struct file_lock *fl)
{
        int error;
        might_sleep();
        for (;;) {
                error = flock_lock_inode(inode, fl);
                if (error != FILE_LOCK_DEFERRED)
                        break;
                error = wait_event_interruptible(fl->fl_wait,
                                list_empty(&fl->fl_blocked_member));
                if (error)
                        break;
        }
        locks_delete_block(fl);
        return error;
}

/**
 * locks_lock_inode_wait - Apply a lock to an inode
 * @inode: inode of the file to apply to
 * @fl: The lock to be applied
 *
 * Apply a POSIX or FLOCK style lock request to an inode.
 */
int locks_lock_inode_wait(struct inode *inode, struct file_lock *fl)
{
        int res = 0;
        switch (fl->fl_flags & (FL_POSIX|FL_FLOCK)) {
                case FL_POSIX:
                        res = posix_lock_inode_wait(inode, fl);
                        break;
                case FL_FLOCK:
                        res = flock_lock_inode_wait(inode, fl);
                        break;
                default:
                        BUG();
        }
        return res;
}
EXPORT_SYMBOL(locks_lock_inode_wait);

/**
 *      sys_flock: - flock() system call.
 *      @fd: the file descriptor to lock.
 *      @cmd: the type of lock to apply.
 *
 *      Apply a %FL_FLOCK style lock to an open file descriptor.
 *      The @cmd can be one of:
 *
 *      - %LOCK_SH -- a shared lock.
 *      - %LOCK_EX -- an exclusive lock.
 *      - %LOCK_UN -- remove an existing lock.
 *      - %LOCK_MAND -- a 'mandatory' flock. (DEPRECATED)
 *
 *      %LOCK_MAND support has been removed from the kernel.
 */
SYSCALL_DEFINE2(flock, unsigned int, fd, unsigned int, cmd)
{
        int can_sleep, error, type;
        struct file_lock fl;
        struct fd f;

        /*
         * LOCK_MAND locks were broken for a long time in that they never
         * conflicted with one another and didn't prevent any sort of open,
         * read or write activity.
         *
         * Just ignore these requests now, to preserve legacy behavior, but
         * throw a warning to let people know that they don't actually work.
         */
        if (cmd & LOCK_MAND) {
                pr_warn_once("%s(%d): Attempt to set a LOCK_MAND lock via flock(2). This support has been removed and the request ignored.\n", current->comm, current->pid);
                return 0;
        }

        type = flock_translate_cmd(cmd & ~LOCK_NB);
        if (type < 0)
                return type;

        error = -EBADF;
        f = fdget(fd);
        if (!f.file)
                return error;

        if (type != F_UNLCK && !(f.file->f_mode & (FMODE_READ | FMODE_WRITE)))
                goto out_putf;

        flock_make_lock(f.file, &fl, type);

        error = security_file_lock(f.file, fl.fl_type);
        if (error)
                goto out_putf;

        can_sleep = !(cmd & LOCK_NB);
        if (can_sleep)
                fl.fl_flags |= FL_SLEEP;

        if (f.file->f_op->flock)
                error = f.file->f_op->flock(f.file,
                                            (can_sleep) ? F_SETLKW : F_SETLK,
                                            &fl);
        else
                error = locks_lock_file_wait(f.file, &fl);

        locks_release_private(&fl);
 out_putf:
        fdput(f);

        return error;
}

/**
 * vfs_test_lock - test file byte range lock
 * @filp: The file to test lock for
 * @fl: The lock to test; also used to hold result
 *
 * Returns -ERRNO on failure.  Indicates presence of conflicting lock by
 * setting conf->fl_type to something other than F_UNLCK.
 */
int vfs_test_lock(struct file *filp, struct file_lock *fl)
{
        WARN_ON_ONCE(filp != fl->fl_file);
        if (filp->f_op->lock)
                return filp->f_op->lock(filp, F_GETLK, fl);
        posix_test_lock(filp, fl);
        return 0;
}
EXPORT_SYMBOL_GPL(vfs_test_lock);

/**
 * locks_translate_pid - translate a file_lock's fl_pid number into a namespace
 * @fl: The file_lock who's fl_pid should be translated
 * @ns: The namespace into which the pid should be translated
 *
 * Used to tranlate a fl_pid into a namespace virtual pid number
 */
static pid_t locks_translate_pid(struct file_lock *fl, struct pid_namespace *ns)
{
        pid_t vnr;
        struct pid *pid;

        if (IS_OFDLCK(fl))
                return -1;
        if (IS_REMOTELCK(fl))
                return fl->fl_pid;
        /*
         * If the flock owner process is dead and its pid has been already
         * freed, the translation below won't work, but we still want to show
         * flock owner pid number in init pidns.
         */
        if (ns == &init_pid_ns)
                return (pid_t)fl->fl_pid;

        rcu_read_lock();
        pid = find_pid_ns(fl->fl_pid, &init_pid_ns);
        vnr = pid_nr_ns(pid, ns);
        rcu_read_unlock();
        return vnr;
}

static int posix_lock_to_flock(struct flock *flock, struct file_lock *fl)
{
        flock->l_pid = locks_translate_pid(fl, task_active_pid_ns(current));
#if BITS_PER_LONG == 32
        /*
         * Make sure we can represent the posix lock via
         * legacy 32bit flock.
         */
        if (fl->fl_start > OFFT_OFFSET_MAX)
                return -EOVERFLOW;
        if (fl->fl_end != OFFSET_MAX && fl->fl_end > OFFT_OFFSET_MAX)
                return -EOVERFLOW;
#endif
        flock->l_start = fl->fl_start;
        flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
                fl->fl_end - fl->fl_start + 1;
        flock->l_whence = 0;
        flock->l_type = fl->fl_type;
        return 0;
}

#if BITS_PER_LONG == 32
static void posix_lock_to_flock64(struct flock64 *flock, struct file_lock *fl)
{
        flock->l_pid = locks_translate_pid(fl, task_active_pid_ns(current));
        flock->l_start = fl->fl_start;
        flock->l_len = fl->fl_end == OFFSET_MAX ? 0 :
                fl->fl_end - fl->fl_start + 1;
        flock->l_whence = 0;
        flock->l_type = fl->fl_type;
}
#endif

/* Report the first existing lock that would conflict with l.
 * This implements the F_GETLK command of fcntl().
 */
int fcntl_getlk(struct file *filp, unsigned int cmd, struct flock *flock)
{
        struct file_lock *fl;
        int error;

        fl = locks_alloc_lock();
        if (fl == NULL)
                return -ENOMEM;
        error = -EINVAL;
        if (flock->l_type != F_RDLCK && flock->l_type != F_WRLCK)
                goto out;

        error = flock_to_posix_lock(filp, fl, flock);
        if (error)
                goto out;

        if (cmd == F_OFD_GETLK) {
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                fl->fl_flags |= FL_OFDLCK;
                fl->fl_owner = filp;
        }

        error = vfs_test_lock(filp, fl);
        if (error)
                goto out;

        flock->l_type = fl->fl_type;
        if (fl->fl_type != F_UNLCK) {
                error = posix_lock_to_flock(flock, fl);
                if (error)
                        goto out;
        }
out:
        locks_free_lock(fl);
        return error;
}

/**
 * vfs_lock_file - file byte range lock
 * @filp: The file to apply the lock to
 * @cmd: type of locking operation (F_SETLK, F_GETLK, etc.)
 * @fl: The lock to be applied
 * @conf: Place to return a copy of the conflicting lock, if found.
 *
 * A caller that doesn't care about the conflicting lock may pass NULL
 * as the final argument.
 *
 * If the filesystem defines a private ->lock() method, then @conf will
 * be left unchanged; so a caller that cares should initialize it to
 * some acceptable default.
 *
 * To avoid blocking kernel daemons, such as lockd, that need to acquire POSIX
 * locks, the ->lock() interface may return asynchronously, before the lock has
 * been granted or denied by the underlying filesystem, if (and only if)
 * lm_grant is set. Callers expecting ->lock() to return asynchronously
 * will only use F_SETLK, not F_SETLKW; they will set FL_SLEEP if (and only if)
 * the request is for a blocking lock. When ->lock() does return asynchronously,
 * it must return FILE_LOCK_DEFERRED, and call ->lm_grant() when the lock
 * request completes.
 * If the request is for non-blocking lock the file system should return
 * FILE_LOCK_DEFERRED then try to get the lock and call the callback routine
 * with the result. If the request timed out the callback routine will return a
 * nonzero return code and the file system should release the lock. The file
 * system is also responsible to keep a corresponding posix lock when it
 * grants a lock so the VFS can find out which locks are locally held and do
 * the correct lock cleanup when required.
 * The underlying filesystem must not drop the kernel lock or call
 * ->lm_grant() before returning to the caller with a FILE_LOCK_DEFERRED
 * return code.
 */
int vfs_lock_file(struct file *filp, unsigned int cmd, struct file_lock *fl, struct file_lock *conf)
{
        WARN_ON_ONCE(filp != fl->fl_file);
        if (filp->f_op->lock)
                return filp->f_op->lock(filp, cmd, fl);
        else
                return posix_lock_file(filp, fl, conf);
}
EXPORT_SYMBOL_GPL(vfs_lock_file);

static int do_lock_file_wait(struct file *filp, unsigned int cmd,
                             struct file_lock *fl)
{
        int error;

        error = security_file_lock(filp, fl->fl_type);
        if (error)
                return error;

        for (;;) {
                error = vfs_lock_file(filp, cmd, fl, NULL);
                if (error != FILE_LOCK_DEFERRED)
                        break;
                error = wait_event_interruptible(fl->fl_wait,
                                        list_empty(&fl->fl_blocked_member));
                if (error)
                        break;
        }
        locks_delete_block(fl);

        return error;
}

/* Ensure that fl->fl_file has compatible f_mode for F_SETLK calls */
static int
check_fmode_for_setlk(struct file_lock *fl)
{
        switch (fl->fl_type) {
        case F_RDLCK:
                if (!(fl->fl_file->f_mode & FMODE_READ))
                        return -EBADF;
                break;
        case F_WRLCK:
                if (!(fl->fl_file->f_mode & FMODE_WRITE))
                        return -EBADF;
        }
        return 0;
}

/* Apply the lock described by l to an open file descriptor.
 * This implements both the F_SETLK and F_SETLKW commands of fcntl().
 */
int fcntl_setlk(unsigned int fd, struct file *filp, unsigned int cmd,
                struct flock *flock)
{
        struct file_lock *file_lock = locks_alloc_lock();
        struct inode *inode = file_inode(filp);
        struct file *f;
        int error;

        if (file_lock == NULL)
                return -ENOLCK;

        error = flock_to_posix_lock(filp, file_lock, flock);
        if (error)
                goto out;

        error = check_fmode_for_setlk(file_lock);
        if (error)
                goto out;

        /*
         * If the cmd is requesting file-private locks, then set the
         * FL_OFDLCK flag and override the owner.
         */
        switch (cmd) {
        case F_OFD_SETLK:
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                cmd = F_SETLK;
                file_lock->fl_flags |= FL_OFDLCK;
                file_lock->fl_owner = filp;
                break;
        case F_OFD_SETLKW:
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                cmd = F_SETLKW;
                file_lock->fl_flags |= FL_OFDLCK;
                file_lock->fl_owner = filp;
                fallthrough;
        case F_SETLKW:
                file_lock->fl_flags |= FL_SLEEP;
        }

        error = do_lock_file_wait(filp, cmd, file_lock);

        /*
         * Attempt to detect a close/fcntl race and recover by releasing the
         * lock that was just acquired. There is no need to do that when we're
         * unlocking though, or for OFD locks.
         */
        if (!error && file_lock->fl_type != F_UNLCK &&
            !(file_lock->fl_flags & FL_OFDLCK)) {
                struct files_struct *files = current->files;
                /*
                 * We need that spin_lock here - it prevents reordering between
                 * update of i_flctx->flc_posix and check for it done in
                 * close(). rcu_read_lock() wouldn't do.
                 */
                spin_lock(&files->file_lock);
                f = files_lookup_fd_locked(files, fd);
                spin_unlock(&files->file_lock);
                if (f != filp) {
                        file_lock->fl_type = F_UNLCK;
                        error = do_lock_file_wait(filp, cmd, file_lock);
                        WARN_ON_ONCE(error);
                        error = -EBADF;
                }
        }
out:
        trace_fcntl_setlk(inode, file_lock, error);
        locks_free_lock(file_lock);
        return error;
}

#if BITS_PER_LONG == 32
/* Report the first existing lock that would conflict with l.
 * This implements the F_GETLK command of fcntl().
 */
int fcntl_getlk64(struct file *filp, unsigned int cmd, struct flock64 *flock)
{
        struct file_lock *fl;
        int error;

        fl = locks_alloc_lock();
        if (fl == NULL)
                return -ENOMEM;

        error = -EINVAL;
        if (flock->l_type != F_RDLCK && flock->l_type != F_WRLCK)
                goto out;

        error = flock64_to_posix_lock(filp, fl, flock);
        if (error)
                goto out;

        if (cmd == F_OFD_GETLK) {
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                fl->fl_flags |= FL_OFDLCK;
                fl->fl_owner = filp;
        }

        error = vfs_test_lock(filp, fl);
        if (error)
                goto out;

        flock->l_type = fl->fl_type;
        if (fl->fl_type != F_UNLCK)
                posix_lock_to_flock64(flock, fl);

out:
        locks_free_lock(fl);
        return error;
}

/* Apply the lock described by l to an open file descriptor.
 * This implements both the F_SETLK and F_SETLKW commands of fcntl().
 */
int fcntl_setlk64(unsigned int fd, struct file *filp, unsigned int cmd,
                struct flock64 *flock)
{
        struct file_lock *file_lock = locks_alloc_lock();
        struct file *f;
        int error;

        if (file_lock == NULL)
                return -ENOLCK;

        error = flock64_to_posix_lock(filp, file_lock, flock);
        if (error)
                goto out;

        error = check_fmode_for_setlk(file_lock);
        if (error)
                goto out;

        /*
         * If the cmd is requesting file-private locks, then set the
         * FL_OFDLCK flag and override the owner.
         */
        switch (cmd) {
        case F_OFD_SETLK:
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                cmd = F_SETLK64;
                file_lock->fl_flags |= FL_OFDLCK;
                file_lock->fl_owner = filp;
                break;
        case F_OFD_SETLKW:
                error = -EINVAL;
                if (flock->l_pid != 0)
                        goto out;

                cmd = F_SETLKW64;
                file_lock->fl_flags |= FL_OFDLCK;
                file_lock->fl_owner = filp;
                fallthrough;
        case F_SETLKW64:
                file_lock->fl_flags |= FL_SLEEP;
        }

        error = do_lock_file_wait(filp, cmd, file_lock);

        /*
         * Attempt to detect a close/fcntl race and recover by releasing the
         * lock that was just acquired. There is no need to do that when we're
         * unlocking though, or for OFD locks.
         */
        if (!error && file_lock->fl_type != F_UNLCK &&
            !(file_lock->fl_flags & FL_OFDLCK)) {
                struct files_struct *files = current->files;
                /*
                 * We need that spin_lock here - it prevents reordering between
                 * update of i_flctx->flc_posix and check for it done in
                 * close(). rcu_read_lock() wouldn't do.
                 */
                spin_lock(&files->file_lock);
                f = files_lookup_fd_locked(files, fd);
                spin_unlock(&files->file_lock);
                if (f != filp) {
                        file_lock->fl_type = F_UNLCK;
                        error = do_lock_file_wait(filp, cmd, file_lock);
                        WARN_ON_ONCE(error);
                        error = -EBADF;
                }
        }
out:
        locks_free_lock(file_lock);
        return error;
}
#endif /* BITS_PER_LONG == 32 */

/*
 * This function is called when the file is being removed
 * from the task's fd array.  POSIX locks belonging to this task
 * are deleted at this time.
 */
void locks_remove_posix(struct file *filp, fl_owner_t owner)
{
        int error;
        struct inode *inode = file_inode(filp);
        struct file_lock lock;
        struct file_lock_context *ctx;

        /*
         * If there are no locks held on this file, we don't need to call
         * posix_lock_file().  Another process could be setting a lock on this
         * file at the same time, but we wouldn't remove that lock anyway.
         */
        ctx = locks_inode_context(inode);
        if (!ctx || list_empty(&ctx->flc_posix))
                return;

        locks_init_lock(&lock);
        lock.fl_type = F_UNLCK;
        lock.fl_flags = FL_POSIX | FL_CLOSE;
        lock.fl_start = 0;
        lock.fl_end = OFFSET_MAX;
        lock.fl_owner = owner;
        lock.fl_pid = current->tgid;
        lock.fl_file = filp;
        lock.fl_ops = NULL;
        lock.fl_lmops = NULL;

        error = vfs_lock_file(filp, F_SETLK, &lock, NULL);

        if (lock.fl_ops && lock.fl_ops->fl_release_private)
                lock.fl_ops->fl_release_private(&lock);
        trace_locks_remove_posix(inode, &lock, error);
}
EXPORT_SYMBOL(locks_remove_posix);

/* The i_flctx must be valid when calling into here */
static void
locks_remove_flock(struct file *filp, struct file_lock_context *flctx)
{
        struct file_lock fl;
        struct inode *inode = file_inode(filp);

        if (list_empty(&flctx->flc_flock))
                return;

        flock_make_lock(filp, &fl, F_UNLCK);
        fl.fl_flags |= FL_CLOSE;

        if (filp->f_op->flock)
                filp->f_op->flock(filp, F_SETLKW, &fl);
        else
                flock_lock_inode(inode, &fl);

        if (fl.fl_ops && fl.fl_ops->fl_release_private)
                fl.fl_ops->fl_release_private(&fl);
}

/* The i_flctx must be valid when calling into here */
static void
locks_remove_lease(struct file *filp, struct file_lock_context *ctx)
{
        struct file_lock *fl, *tmp;
        LIST_HEAD(dispose);

        if (list_empty(&ctx->flc_lease))
                return;

        percpu_down_read(&file_rwsem);
        spin_lock(&ctx->flc_lock);
        list_for_each_entry_safe(fl, tmp, &ctx->flc_lease, fl_list)
                if (filp == fl->fl_file)
                        lease_modify(fl, F_UNLCK, &dispose);
        spin_unlock(&ctx->flc_lock);
        percpu_up_read(&file_rwsem);

        locks_dispose_list(&dispose);
}

/*
 * This function is called on the last close of an open file.
 */
void locks_remove_file(struct file *filp)
{
        struct file_lock_context *ctx;

        ctx = locks_inode_context(file_inode(filp));
        if (!ctx)
                return;

        /* remove any OFD locks */
        locks_remove_posix(filp, filp);

        /* remove flock locks */
        locks_remove_flock(filp, ctx);

        /* remove any leases */
        locks_remove_lease(filp, ctx);

        spin_lock(&ctx->flc_lock);
        locks_check_ctx_file_list(filp, &ctx->flc_posix, "POSIX");
        locks_check_ctx_file_list(filp, &ctx->flc_flock, "FLOCK");
        locks_check_ctx_file_list(filp, &ctx->flc_lease, "LEASE");
        spin_unlock(&ctx->flc_lock);
}

/**
 * vfs_cancel_lock - file byte range unblock lock
 * @filp: The file to apply the unblock to
 * @fl: The lock to be unblocked
 *
 * Used by lock managers to cancel blocked requests
 */
int vfs_cancel_lock(struct file *filp, struct file_lock *fl)
{
        WARN_ON_ONCE(filp != fl->fl_file);
        if (filp->f_op->lock)
                return filp->f_op->lock(filp, F_CANCELLK, fl);
        return 0;
}
EXPORT_SYMBOL_GPL(vfs_cancel_lock);

/**
 * vfs_inode_has_locks - are any file locks held on @inode?
 * @inode: inode to check for locks
 *
 * Return true if there are any FL_POSIX or FL_FLOCK locks currently
 * set on @inode.
 */
bool vfs_inode_has_locks(struct inode *inode)
{
        struct file_lock_context *ctx;
        bool ret;

        ctx = locks_inode_context(inode);
        if (!ctx)
                return false;

        spin_lock(&ctx->flc_lock);
        ret = !list_empty(&ctx->flc_posix) || !list_empty(&ctx->flc_flock);
        spin_unlock(&ctx->flc_lock);
        return ret;
}
EXPORT_SYMBOL_GPL(vfs_inode_has_locks);

#ifdef CONFIG_PROC_FS
#include <linux/proc_fs.h>
#include <linux/seq_file.h>

struct locks_iterator {
        int     li_cpu;
        loff_t  li_pos;
};

static void lock_get_status(struct seq_file *f, struct file_lock *fl,
                            loff_t id, char *pfx, int repeat)
{
        struct inode *inode = NULL;
        unsigned int fl_pid;
        struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
        int type;

        fl_pid = locks_translate_pid(fl, proc_pidns);
        /*
         * If lock owner is dead (and pid is freed) or not visible in current
         * pidns, zero is shown as a pid value. Check lock info from
         * init_pid_ns to get saved lock pid value.
         */

        if (fl->fl_file != NULL)
                inode = file_inode(fl->fl_file);

        seq_printf(f, "%lld: ", id);

        if (repeat)
                seq_printf(f, "%*s", repeat - 1 + (int)strlen(pfx), pfx);

        if (IS_POSIX(fl)) {
                if (fl->fl_flags & FL_ACCESS)
                        seq_puts(f, "ACCESS");
                else if (IS_OFDLCK(fl))
                        seq_puts(f, "OFDLCK");
                else
                        seq_puts(f, "POSIX ");

                seq_printf(f, " %s ",
                             (inode == NULL) ? "*NOINODE*" : "ADVISORY ");
        } else if (IS_FLOCK(fl)) {
                seq_puts(f, "FLOCK  ADVISORY  ");
        } else if (IS_LEASE(fl)) {
                if (fl->fl_flags & FL_DELEG)
                        seq_puts(f, "DELEG  ");
                else
                        seq_puts(f, "LEASE  ");

                if (lease_breaking(fl))
                        seq_puts(f, "BREAKING  ");
                else if (fl->fl_file)
                        seq_puts(f, "ACTIVE    ");
                else
                        seq_puts(f, "BREAKER   ");
        } else {
                seq_puts(f, "UNKNOWN UNKNOWN  ");
        }
        type = IS_LEASE(fl) ? target_leasetype(fl) : fl->fl_type;

        seq_printf(f, "%s ", (type == F_WRLCK) ? "WRITE" :
                             (type == F_RDLCK) ? "READ" : "UNLCK");
        if (inode) {
                /* userspace relies on this representation of dev_t */
                seq_printf(f, "%d %02x:%02x:%lu ", fl_pid,
                                MAJOR(inode->i_sb->s_dev),
                                MINOR(inode->i_sb->s_dev), inode->i_ino);
        } else {
                seq_printf(f, "%d <none>:0 ", fl_pid);
        }
        if (IS_POSIX(fl)) {
                if (fl->fl_end == OFFSET_MAX)
                        seq_printf(f, "%Ld EOF\n", fl->fl_start);
                else
                        seq_printf(f, "%Ld %Ld\n", fl->fl_start, fl->fl_end);
        } else {
                seq_puts(f, "0 EOF\n");
        }
}

static struct file_lock *get_next_blocked_member(struct file_lock *node)
{
        struct file_lock *tmp;

        /* NULL node or root node */
        if (node == NULL || node->fl_blocker == NULL)
                return NULL;

        /* Next member in the linked list could be itself */
        tmp = list_next_entry(node, fl_blocked_member);
        if (list_entry_is_head(tmp, &node->fl_blocker->fl_blocked_requests, fl_blocked_member)
                || tmp == node) {
                return NULL;
        }

        return tmp;
}

static int locks_show(struct seq_file *f, void *v)
{
        struct locks_iterator *iter = f->private;
        struct file_lock *cur, *tmp;
        struct pid_namespace *proc_pidns = proc_pid_ns(file_inode(f->file)->i_sb);
        int level = 0;

        cur = hlist_entry(v, struct file_lock, fl_link);

        if (locks_translate_pid(cur, proc_pidns) == 0)
                return 0;

        /* View this crossed linked list as a binary tree, the first member of fl_blocked_requests
         * is the left child of current node, the next silibing in fl_blocked_member is the
         * right child, we can alse get the parent of current node from fl_blocker, so this
         * question becomes traversal of a binary tree
         */
        while (cur != NULL) {
                if (level)
                        lock_get_status(f, cur, iter->li_pos, "-> ", level);
                else
                        lock_get_status(f, cur, iter->li_pos, "", level);

                if (!list_empty(&cur->fl_blocked_requests)) {
                        /* Turn left */
                        cur = list_first_entry_or_null(&cur->fl_blocked_requests,
                                struct file_lock, fl_blocked_member);
                        level++;
                } else {
                        /* Turn right */
                        tmp = get_next_blocked_member(cur);
                        /* Fall back to parent node */
                        while (tmp == NULL && cur->fl_blocker != NULL) {
                                cur = cur->fl_blocker;
                                level--;
                                tmp = get_next_blocked_member(cur);
                        }
                        cur = tmp;
                }
        }

        return 0;
}

static void __show_fd_locks(struct seq_file *f,
                        struct list_head *head, int *id,
                        struct file *filp, struct files_struct *files)
{
        struct file_lock *fl;

        list_for_each_entry(fl, head, fl_list) {

                if (filp != fl->fl_file)
                        continue;
                if (fl->fl_owner != files &&
                    fl->fl_owner != filp)
                        continue;

                (*id)++;
                seq_puts(f, "lock:\t");
                lock_get_status(f, fl, *id, "", 0);
        }
}

void show_fd_locks(struct seq_file *f,
                  struct file *filp, struct files_struct *files)
{
        struct inode *inode = file_inode(filp);
        struct file_lock_context *ctx;
        int id = 0;

        ctx = locks_inode_context(inode);
        if (!ctx)
                return;

        spin_lock(&ctx->flc_lock);
        __show_fd_locks(f, &ctx->flc_flock, &id, filp, files);
        __show_fd_locks(f, &ctx->flc_posix, &id, filp, files);
        __show_fd_locks(f, &ctx->flc_lease, &id, filp, files);
        spin_unlock(&ctx->flc_lock);
}

static void *locks_start(struct seq_file *f, loff_t *pos)
        __acquires(&blocked_lock_lock)
{
        struct locks_iterator *iter = f->private;

        iter->li_pos = *pos + 1;
        percpu_down_write(&file_rwsem);
        spin_lock(&blocked_lock_lock);
        return seq_hlist_start_percpu(&file_lock_list.hlist, &iter->li_cpu, *pos);
}

static void *locks_next(struct seq_file *f, void *v, loff_t *pos)
{
        struct locks_iterator *iter = f->private;

        ++iter->li_pos;
        return seq_hlist_next_percpu(v, &file_lock_list.hlist, &iter->li_cpu, pos);
}

static void locks_stop(struct seq_file *f, void *v)
        __releases(&blocked_lock_lock)
{
        spin_unlock(&blocked_lock_lock);
        percpu_up_write(&file_rwsem);
}

static const struct seq_operations locks_seq_operations = {
        .start  = locks_start,
        .next   = locks_next,
        .stop   = locks_stop,
        .show   = locks_show,
};

static int __init proc_locks_init(void)
{
        proc_create_seq_private("locks", 0, NULL, &locks_seq_operations,
                        sizeof(struct locks_iterator), NULL);
        return 0;
}
fs_initcall(proc_locks_init);
#endif

static int __init filelock_init(void)
{
        int i;

        flctx_cache = kmem_cache_create("file_lock_ctx",
                        sizeof(struct file_lock_context), 0, SLAB_PANIC, NULL);

        filelock_cache = kmem_cache_create("file_lock_cache",
                        sizeof(struct file_lock), 0, SLAB_PANIC, NULL);

        for_each_possible_cpu(i) {
                struct file_lock_list_struct *fll = per_cpu_ptr(&file_lock_list, i);

                spin_lock_init(&fll->lock);
                INIT_HLIST_HEAD(&fll->hlist);
        }

        lease_notifier_chain_init();
        return 0;
}
core_initcall(filelock_init);