NFS: Fix use after free in write error path

[linux-block.git] / fs / nfs / write.c

/*
 * linux/fs/nfs/write.c
 *
 * Write file data over NFS.
 *
 * Copyright (C) 1996, 1997, Olaf Kirch <okir@monad.swb.de>
 */

#include <linux/types.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/pagemap.h>
#include <linux/file.h>
#include <linux/writeback.h>
#include <linux/swap.h>
#include <linux/migrate.h>

#include <linux/sunrpc/clnt.h>
#include <linux/nfs_fs.h>
#include <linux/nfs_mount.h>
#include <linux/nfs_page.h>
#include <linux/backing-dev.h>
#include <linux/export.h>
#include <linux/freezer.h>
#include <linux/wait.h>

#include <linux/uaccess.h>

#include "delegation.h"
#include "internal.h"
#include "iostat.h"
#include "nfs4_fs.h"
#include "fscache.h"
#include "pnfs.h"

#include "nfstrace.h"

#define NFSDBG_FACILITY         NFSDBG_PAGECACHE

#define MIN_POOL_WRITE          (32)
#define MIN_POOL_COMMIT         (4)

/*
 * Local function declarations
 */
static void nfs_redirty_request(struct nfs_page *req);
static const struct rpc_call_ops nfs_commit_ops;
static const struct nfs_pgio_completion_ops nfs_async_write_completion_ops;
static const struct nfs_commit_completion_ops nfs_commit_completion_ops;
static const struct nfs_rw_ops nfs_rw_write_ops;
static void nfs_clear_request_commit(struct nfs_page *req);
static void nfs_init_cinfo_from_inode(struct nfs_commit_info *cinfo,
                                      struct inode *inode);
static struct nfs_page *
nfs_page_search_commits_for_head_request_locked(struct nfs_inode *nfsi,
                                                struct page *page);

static struct kmem_cache *nfs_wdata_cachep;
static mempool_t *nfs_wdata_mempool;
static struct kmem_cache *nfs_cdata_cachep;
static mempool_t *nfs_commit_mempool;

struct nfs_commit_data *nfs_commitdata_alloc(bool never_fail)
{
        struct nfs_commit_data *p;

        if (never_fail)
                p = mempool_alloc(nfs_commit_mempool, GFP_NOIO);
        else {
                /* It is OK to do some reclaim, not no safe to wait
                 * for anything to be returned to the pool.
                 * mempool_alloc() cannot handle that particular combination,
                 * so we need two separate attempts.
                 */
                p = mempool_alloc(nfs_commit_mempool, GFP_NOWAIT);
                if (!p)
                        p = kmem_cache_alloc(nfs_cdata_cachep, GFP_NOIO |
                                             __GFP_NOWARN | __GFP_NORETRY);
                if (!p)
                        return NULL;
        }

        memset(p, 0, sizeof(*p));
        INIT_LIST_HEAD(&p->pages);
        return p;
}
EXPORT_SYMBOL_GPL(nfs_commitdata_alloc);

void nfs_commit_free(struct nfs_commit_data *p)
{
        mempool_free(p, nfs_commit_mempool);
}
EXPORT_SYMBOL_GPL(nfs_commit_free);

static struct nfs_pgio_header *nfs_writehdr_alloc(void)
{
        struct nfs_pgio_header *p = mempool_alloc(nfs_wdata_mempool, GFP_NOIO);

        memset(p, 0, sizeof(*p));
        return p;
}

static void nfs_writehdr_free(struct nfs_pgio_header *hdr)
{
        mempool_free(hdr, nfs_wdata_mempool);
}

static void nfs_context_set_write_error(struct nfs_open_context *ctx, int error)
{
        ctx->error = error;
        smp_wmb();
        set_bit(NFS_CONTEXT_ERROR_WRITE, &ctx->flags);
}

/*
 * nfs_page_find_head_request_locked - find head request associated with @page
 *
 * must be called while holding the inode lock.
 *
 * returns matching head request with reference held, or NULL if not found.
 */
static struct nfs_page *
nfs_page_find_head_request_locked(struct nfs_inode *nfsi, struct page *page)
{
        struct nfs_page *req = NULL;

        if (PagePrivate(page))
                req = (struct nfs_page *)page_private(page);
        else if (unlikely(PageSwapCache(page)))
                req = nfs_page_search_commits_for_head_request_locked(nfsi,
                        page);

        if (req) {
                WARN_ON_ONCE(req->wb_head != req);
                kref_get(&req->wb_kref);
        }

        return req;
}

/*
 * nfs_page_find_head_request - find head request associated with @page
 *
 * returns matching head request with reference held, or NULL if not found.
 */
static struct nfs_page *nfs_page_find_head_request(struct page *page)
{
        struct inode *inode = page_file_mapping(page)->host;
        struct nfs_page *req = NULL;

        spin_lock(&inode->i_lock);
        req = nfs_page_find_head_request_locked(NFS_I(inode), page);
        spin_unlock(&inode->i_lock);
        return req;
}

/* Adjust the file length if we're writing beyond the end */
static void nfs_grow_file(struct page *page, unsigned int offset, unsigned int count)
{
        struct inode *inode = page_file_mapping(page)->host;
        loff_t end, i_size;
        pgoff_t end_index;

        spin_lock(&inode->i_lock);
        i_size = i_size_read(inode);
        end_index = (i_size - 1) >> PAGE_SHIFT;
        if (i_size > 0 && page_index(page) < end_index)
                goto out;
        end = page_file_offset(page) + ((loff_t)offset+count);
        if (i_size >= end)
                goto out;
        i_size_write(inode, end);
        nfs_inc_stats(inode, NFSIOS_EXTENDWRITE);
out:
        spin_unlock(&inode->i_lock);
}

/* A writeback failed: mark the page as bad, and invalidate the page cache */
static void nfs_set_pageerror(struct page *page)
{
        nfs_zap_mapping(page_file_mapping(page)->host, page_file_mapping(page));
}

/*
 * nfs_page_group_search_locked
 * @head - head request of page group
 * @page_offset - offset into page
 *
 * Search page group with head @head to find a request that contains the
 * page offset @page_offset.
 *
 * Returns a pointer to the first matching nfs request, or NULL if no
 * match is found.
 *
 * Must be called with the page group lock held
 */
static struct nfs_page *
nfs_page_group_search_locked(struct nfs_page *head, unsigned int page_offset)
{
        struct nfs_page *req;

        WARN_ON_ONCE(head != head->wb_head);
        WARN_ON_ONCE(!test_bit(PG_HEADLOCK, &head->wb_head->wb_flags));

        req = head;
        do {
                if (page_offset >= req->wb_pgbase &&
                    page_offset < (req->wb_pgbase + req->wb_bytes))
                        return req;

                req = req->wb_this_page;
        } while (req != head);

        return NULL;
}

/*
 * nfs_page_group_covers_page
 * @head - head request of page group
 *
 * Return true if the page group with head @head covers the whole page,
 * returns false otherwise
 */
static bool nfs_page_group_covers_page(struct nfs_page *req)
{
        struct nfs_page *tmp;
        unsigned int pos = 0;
        unsigned int len = nfs_page_length(req->wb_page);

        nfs_page_group_lock(req, false);

        do {
                tmp = nfs_page_group_search_locked(req->wb_head, pos);
                if (tmp) {
                        /* no way this should happen */
                        WARN_ON_ONCE(tmp->wb_pgbase != pos);
                        pos += tmp->wb_bytes - (pos - tmp->wb_pgbase);
                }
        } while (tmp && pos < len);

        nfs_page_group_unlock(req);
        WARN_ON_ONCE(pos > len);
        return pos == len;
}

/* We can set the PG_uptodate flag if we see that a write request
 * covers the full page.
 */
static void nfs_mark_uptodate(struct nfs_page *req)
{
        if (PageUptodate(req->wb_page))
                return;
        if (!nfs_page_group_covers_page(req))
                return;
        SetPageUptodate(req->wb_page);
}

static int wb_priority(struct writeback_control *wbc)
{
        int ret = 0;

        if (wbc->sync_mode == WB_SYNC_ALL)
                ret = FLUSH_COND_STABLE;
        return ret;
}

/*
 * NFS congestion control
 */

int nfs_congestion_kb;

#define NFS_CONGESTION_ON_THRESH        (nfs_congestion_kb >> (PAGE_SHIFT-10))
#define NFS_CONGESTION_OFF_THRESH       \
        (NFS_CONGESTION_ON_THRESH - (NFS_CONGESTION_ON_THRESH >> 2))

static void nfs_set_page_writeback(struct page *page)
{
        struct nfs_server *nfss = NFS_SERVER(page_file_mapping(page)->host);
        int ret = test_set_page_writeback(page);

        WARN_ON_ONCE(ret != 0);

        if (atomic_long_inc_return(&nfss->writeback) >
                        NFS_CONGESTION_ON_THRESH) {
                set_bdi_congested(&nfss->backing_dev_info,
                                        BLK_RW_ASYNC);
        }
}

static void nfs_end_page_writeback(struct nfs_page *req)
{
        struct inode *inode = page_file_mapping(req->wb_page)->host;
        struct nfs_server *nfss = NFS_SERVER(inode);

        if (!nfs_page_group_sync_on_bit(req, PG_WB_END))
                return;

        end_page_writeback(req->wb_page);
        if (atomic_long_dec_return(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
                clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);
}


/* nfs_page_group_clear_bits
 *   @req - an nfs request
 * clears all page group related bits from @req
 */
static void
nfs_page_group_clear_bits(struct nfs_page *req)
{
        clear_bit(PG_TEARDOWN, &req->wb_flags);
        clear_bit(PG_UNLOCKPAGE, &req->wb_flags);
        clear_bit(PG_UPTODATE, &req->wb_flags);
        clear_bit(PG_WB_END, &req->wb_flags);
        clear_bit(PG_REMOVE, &req->wb_flags);
}


/*
 * nfs_unroll_locks_and_wait -  unlock all newly locked reqs and wait on @req
 *
 * this is a helper function for nfs_lock_and_join_requests
 *
 * @inode - inode associated with request page group, must be holding inode lock
 * @head  - head request of page group, must be holding head lock
 * @req   - request that couldn't lock and needs to wait on the req bit lock
 * @nonblock - if true, don't actually wait
 *
 * NOTE: this must be called holding page_group bit lock and inode spin lock
 *       and BOTH will be released before returning.
 *
 * returns 0 on success, < 0 on error.
 */
static int
nfs_unroll_locks_and_wait(struct inode *inode, struct nfs_page *head,
                          struct nfs_page *req, bool nonblock)
        __releases(&inode->i_lock)
{
        struct nfs_page *tmp;
        int ret;

        /* relinquish all the locks successfully grabbed this run */
        for (tmp = head ; tmp != req; tmp = tmp->wb_this_page)
                nfs_unlock_request(tmp);

        WARN_ON_ONCE(test_bit(PG_TEARDOWN, &req->wb_flags));

        /* grab a ref on the request that will be waited on */
        kref_get(&req->wb_kref);

        nfs_page_group_unlock(head);
        spin_unlock(&inode->i_lock);

        /* release ref from nfs_page_find_head_request_locked */
        nfs_release_request(head);

        if (!nonblock)
                ret = nfs_wait_on_request(req);
        else
                ret = -EAGAIN;
        nfs_release_request(req);

        return ret;
}

/*
 * nfs_destroy_unlinked_subrequests - destroy recently unlinked subrequests
 *
 * @destroy_list - request list (using wb_this_page) terminated by @old_head
 * @old_head - the old head of the list
 *
 * All subrequests must be locked and removed from all lists, so at this point
 * they are only "active" in this function, and possibly in nfs_wait_on_request
 * with a reference held by some other context.
 */
static void
nfs_destroy_unlinked_subrequests(struct nfs_page *destroy_list,
                                 struct nfs_page *old_head)
{
        while (destroy_list) {
                struct nfs_page *subreq = destroy_list;

                destroy_list = (subreq->wb_this_page == old_head) ?
                                   NULL : subreq->wb_this_page;

                WARN_ON_ONCE(old_head != subreq->wb_head);

                /* make sure old group is not used */
                subreq->wb_head = subreq;
                subreq->wb_this_page = subreq;

                /* subreq is now totally disconnected from page group or any
                 * write / commit lists. last chance to wake any waiters */
                nfs_unlock_request(subreq);

                if (!test_bit(PG_TEARDOWN, &subreq->wb_flags)) {
                        /* release ref on old head request */
                        nfs_release_request(old_head);

                        nfs_page_group_clear_bits(subreq);

                        /* release the PG_INODE_REF reference */
                        if (test_and_clear_bit(PG_INODE_REF, &subreq->wb_flags))
                                nfs_release_request(subreq);
                        else
                                WARN_ON_ONCE(1);
                } else {
                        WARN_ON_ONCE(test_bit(PG_CLEAN, &subreq->wb_flags));
                        /* zombie requests have already released the last
                         * reference and were waiting on the rest of the
                         * group to complete. Since it's no longer part of a
                         * group, simply free the request */
                        nfs_page_group_clear_bits(subreq);
                        nfs_free_request(subreq);
                }
        }
}

/*
 * nfs_lock_and_join_requests - join all subreqs to the head req and return
 *                              a locked reference, cancelling any pending
 *                              operations for this page.
 *
 * @page - the page used to lookup the "page group" of nfs_page structures
 * @nonblock - if true, don't block waiting for request locks
 *
 * This function joins all sub requests to the head request by first
 * locking all requests in the group, cancelling any pending operations
 * and finally updating the head request to cover the whole range covered by
 * the (former) group.  All subrequests are removed from any write or commit
 * lists, unlinked from the group and destroyed.
 *
 * Returns a locked, referenced pointer to the head request - which after
 * this call is guaranteed to be the only request associated with the page.
 * Returns NULL if no requests are found for @page, or a ERR_PTR if an
 * error was encountered.
 */
static struct nfs_page *
nfs_lock_and_join_requests(struct page *page, bool nonblock)
{
        struct inode *inode = page_file_mapping(page)->host;
        struct nfs_page *head, *subreq;
        struct nfs_page *destroy_list = NULL;
        unsigned int total_bytes;
        int ret;

try_again:
        total_bytes = 0;

        WARN_ON_ONCE(destroy_list);

        spin_lock(&inode->i_lock);

        /*
         * A reference is taken only on the head request which acts as a
         * reference to the whole page group - the group will not be destroyed
         * until the head reference is released.
         */
        head = nfs_page_find_head_request_locked(NFS_I(inode), page);

        if (!head) {
                spin_unlock(&inode->i_lock);
                return NULL;
        }

        /* holding inode lock, so always make a non-blocking call to try the
         * page group lock */
        ret = nfs_page_group_lock(head, true);
        if (ret < 0) {
                spin_unlock(&inode->i_lock);

                if (!nonblock && ret == -EAGAIN) {
                        nfs_page_group_lock_wait(head);
                        nfs_release_request(head);
                        goto try_again;
                }

                nfs_release_request(head);
                return ERR_PTR(ret);
        }

        /* lock each request in the page group */
        subreq = head;
        do {
                /*
                 * Subrequests are always contiguous, non overlapping
                 * and in order - but may be repeated (mirrored writes).
                 */
                if (subreq->wb_offset == (head->wb_offset + total_bytes)) {
                        /* keep track of how many bytes this group covers */
                        total_bytes += subreq->wb_bytes;
                } else if (WARN_ON_ONCE(subreq->wb_offset < head->wb_offset ||
                            ((subreq->wb_offset + subreq->wb_bytes) >
                             (head->wb_offset + total_bytes)))) {
                        nfs_page_group_unlock(head);
                        spin_unlock(&inode->i_lock);
                        return ERR_PTR(-EIO);
                }

                if (!nfs_lock_request(subreq)) {
                        /* releases page group bit lock and
                         * inode spin lock and all references */
                        ret = nfs_unroll_locks_and_wait(inode, head,
                                subreq, nonblock);

                        if (ret == 0)
                                goto try_again;

                        return ERR_PTR(ret);
                }

                subreq = subreq->wb_this_page;
        } while (subreq != head);

        /* Now that all requests are locked, make sure they aren't on any list.
         * Commit list removal accounting is done after locks are dropped */
        subreq = head;
        do {
                nfs_clear_request_commit(subreq);
                subreq = subreq->wb_this_page;
        } while (subreq != head);

        /* unlink subrequests from head, destroy them later */
        if (head->wb_this_page != head) {
                /* destroy list will be terminated by head */
                destroy_list = head->wb_this_page;
                head->wb_this_page = head;

                /* change head request to cover whole range that
                 * the former page group covered */
                head->wb_bytes = total_bytes;
        }

        /*
         * prepare head request to be added to new pgio descriptor
         */
        nfs_page_group_clear_bits(head);

        /*
         * some part of the group was still on the inode list - otherwise
         * the group wouldn't be involved in async write.
         * grab a reference for the head request, iff it needs one.
         */
        if (!test_and_set_bit(PG_INODE_REF, &head->wb_flags))
                kref_get(&head->wb_kref);

        nfs_page_group_unlock(head);

        /* drop lock to clean uprequests on destroy list */
        spin_unlock(&inode->i_lock);

        nfs_destroy_unlinked_subrequests(destroy_list, head);

        /* still holds ref on head from nfs_page_find_head_request_locked
         * and still has lock on head from lock loop */
        return head;
}

static void nfs_write_error_remove_page(struct nfs_page *req)
{
        nfs_unlock_request(req);
        nfs_end_page_writeback(req);
        generic_error_remove_page(page_file_mapping(req->wb_page),
                                  req->wb_page);
        nfs_release_request(req);
}

/*
 * Find an associated nfs write request, and prepare to flush it out
 * May return an error if the user signalled nfs_wait_on_request().
 */
static int nfs_page_async_flush(struct nfs_pageio_descriptor *pgio,
                                struct page *page, bool nonblock,
                                bool launder)
{
        struct nfs_page *req;
        int ret = 0;

        req = nfs_lock_and_join_requests(page, nonblock);
        if (!req)
                goto out;
        ret = PTR_ERR(req);
        if (IS_ERR(req))
                goto out;

        nfs_set_page_writeback(page);
        WARN_ON_ONCE(test_bit(PG_CLEAN, &req->wb_flags));

        ret = 0;
        if (!nfs_pageio_add_request(pgio, req)) {
                ret = pgio->pg_error;
                /*
                 * Remove the problematic req upon fatal errors
                 * in launder case, while other dirty pages can
                 * still be around until they get flushed.
                 */
                if (nfs_error_is_fatal(ret)) {
                        nfs_context_set_write_error(req->wb_context, ret);
                        if (launder) {
                                nfs_write_error_remove_page(req);
                                goto out;
                        }
                }
                nfs_redirty_request(req);
                ret = -EAGAIN;
        } else
                nfs_add_stats(page_file_mapping(page)->host,
                                NFSIOS_WRITEPAGES, 1);
out:
        return ret;
}

static int nfs_do_writepage(struct page *page, struct writeback_control *wbc,
                            struct nfs_pageio_descriptor *pgio, bool launder)
{
        int ret;

        nfs_pageio_cond_complete(pgio, page_index(page));
        ret = nfs_page_async_flush(pgio, page, wbc->sync_mode == WB_SYNC_NONE,
                                   launder);
        if (ret == -EAGAIN) {
                redirty_page_for_writepage(wbc, page);
                ret = 0;
        }
        return ret;
}

/*
 * Write an mmapped page to the server.
 */
static int nfs_writepage_locked(struct page *page,
                                struct writeback_control *wbc,
                                bool launder)
{
        struct nfs_pageio_descriptor pgio;
        struct inode *inode = page_file_mapping(page)->host;
        int err;

        nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGE);
        nfs_pageio_init_write(&pgio, inode, 0,
                                false, &nfs_async_write_completion_ops);
        err = nfs_do_writepage(page, wbc, &pgio, launder);
        nfs_pageio_complete(&pgio);
        if (err < 0)
                return err;
        if (pgio.pg_error < 0)
                return pgio.pg_error;
        return 0;
}

int nfs_writepage(struct page *page, struct writeback_control *wbc)
{
        int ret;

        ret = nfs_writepage_locked(page, wbc, false);
        unlock_page(page);
        return ret;
}

static int nfs_writepages_callback(struct page *page, struct writeback_control *wbc, void *data)
{
        int ret;

        ret = nfs_do_writepage(page, wbc, data, false);
        unlock_page(page);
        return ret;
}

int nfs_writepages(struct address_space *mapping, struct writeback_control *wbc)
{
        struct inode *inode = mapping->host;
        struct nfs_pageio_descriptor pgio;
        int err;

        nfs_inc_stats(inode, NFSIOS_VFSWRITEPAGES);

        nfs_pageio_init_write(&pgio, inode, wb_priority(wbc), false,
                                &nfs_async_write_completion_ops);
        err = write_cache_pages(mapping, wbc, nfs_writepages_callback, &pgio);
        nfs_pageio_complete(&pgio);

        if (err < 0)
                goto out_err;
        err = pgio.pg_error;
        if (err < 0)
                goto out_err;
        return 0;
out_err:
        return err;
}

/*
 * Insert a write request into an inode
 */
static void nfs_inode_add_request(struct inode *inode, struct nfs_page *req)
{
        struct nfs_inode *nfsi = NFS_I(inode);

        WARN_ON_ONCE(req->wb_this_page != req);

        /* Lock the request! */
        nfs_lock_request(req);

        spin_lock(&inode->i_lock);
        if (!nfsi->nrequests &&
            NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
                inode->i_version++;
        /*
         * Swap-space should not get truncated. Hence no need to plug the race
         * with invalidate/truncate.
         */
        if (likely(!PageSwapCache(req->wb_page))) {
                set_bit(PG_MAPPED, &req->wb_flags);
                SetPagePrivate(req->wb_page);
                set_page_private(req->wb_page, (unsigned long)req);
        }
        nfsi->nrequests++;
        /* this a head request for a page group - mark it as having an
         * extra reference so sub groups can follow suit.
         * This flag also informs pgio layer when to bump nrequests when
         * adding subrequests. */
        WARN_ON(test_and_set_bit(PG_INODE_REF, &req->wb_flags));
        kref_get(&req->wb_kref);
        spin_unlock(&inode->i_lock);
}

/*
 * Remove a write request from an inode
 */
static void nfs_inode_remove_request(struct nfs_page *req)
{
        struct inode *inode = d_inode(req->wb_context->dentry);
        struct nfs_inode *nfsi = NFS_I(inode);
        struct nfs_page *head;

        if (nfs_page_group_sync_on_bit(req, PG_REMOVE)) {
                head = req->wb_head;

                spin_lock(&inode->i_lock);
                if (likely(head->wb_page && !PageSwapCache(head->wb_page))) {
                        set_page_private(head->wb_page, 0);
                        ClearPagePrivate(head->wb_page);
                        clear_bit(PG_MAPPED, &head->wb_flags);
                }
                nfsi->nrequests--;
                spin_unlock(&inode->i_lock);
        } else {
                spin_lock(&inode->i_lock);
                nfsi->nrequests--;
                spin_unlock(&inode->i_lock);
        }

        if (test_and_clear_bit(PG_INODE_REF, &req->wb_flags))
                nfs_release_request(req);
}

static void
nfs_mark_request_dirty(struct nfs_page *req)
{
        if (req->wb_page)
                __set_page_dirty_nobuffers(req->wb_page);
}

/*
 * nfs_page_search_commits_for_head_request_locked
 *
 * Search through commit lists on @inode for the head request for @page.
 * Must be called while holding the inode (which is cinfo) lock.
 *
 * Returns the head request if found, or NULL if not found.
 */
static struct nfs_page *
nfs_page_search_commits_for_head_request_locked(struct nfs_inode *nfsi,
                                                struct page *page)
{
        struct nfs_page *freq, *t;
        struct nfs_commit_info cinfo;
        struct inode *inode = &nfsi->vfs_inode;

        nfs_init_cinfo_from_inode(&cinfo, inode);

        /* search through pnfs commit lists */
        freq = pnfs_search_commit_reqs(inode, &cinfo, page);
        if (freq)
                return freq->wb_head;

        /* Linearly search the commit list for the correct request */
        list_for_each_entry_safe(freq, t, &cinfo.mds->list, wb_list) {
                if (freq->wb_page == page)
                        return freq->wb_head;
        }

        return NULL;
}

/**
 * nfs_request_add_commit_list_locked - add request to a commit list
 * @req: pointer to a struct nfs_page
 * @dst: commit list head
 * @cinfo: holds list lock and accounting info
 *
 * This sets the PG_CLEAN bit, updates the cinfo count of
 * number of outstanding requests requiring a commit as well as
 * the MM page stats.
 *
 * The caller must hold cinfo->inode->i_lock, and the nfs_page lock.
 */
void
nfs_request_add_commit_list_locked(struct nfs_page *req, struct list_head *dst,
                            struct nfs_commit_info *cinfo)
{
        set_bit(PG_CLEAN, &req->wb_flags);
        nfs_list_add_request(req, dst);
        cinfo->mds->ncommit++;
}
EXPORT_SYMBOL_GPL(nfs_request_add_commit_list_locked);

/**
 * nfs_request_add_commit_list - add request to a commit list
 * @req: pointer to a struct nfs_page
 * @dst: commit list head
 * @cinfo: holds list lock and accounting info
 *
 * This sets the PG_CLEAN bit, updates the cinfo count of
 * number of outstanding requests requiring a commit as well as
 * the MM page stats.
 *
 * The caller must _not_ hold the cinfo->lock, but must be
 * holding the nfs_page lock.
 */
void
nfs_request_add_commit_list(struct nfs_page *req, struct nfs_commit_info *cinfo)
{
        spin_lock(&cinfo->inode->i_lock);
        nfs_request_add_commit_list_locked(req, &cinfo->mds->list, cinfo);
        spin_unlock(&cinfo->inode->i_lock);
        if (req->wb_page)
                nfs_mark_page_unstable(req->wb_page, cinfo);
}
EXPORT_SYMBOL_GPL(nfs_request_add_commit_list);

/**
 * nfs_request_remove_commit_list - Remove request from a commit list
 * @req: pointer to a nfs_page
 * @cinfo: holds list lock and accounting info
 *
 * This clears the PG_CLEAN bit, and updates the cinfo's count of
 * number of outstanding requests requiring a commit
 * It does not update the MM page stats.
 *
 * The caller _must_ hold the cinfo->lock and the nfs_page lock.
 */
void
nfs_request_remove_commit_list(struct nfs_page *req,
                               struct nfs_commit_info *cinfo)
{
        if (!test_and_clear_bit(PG_CLEAN, &(req)->wb_flags))
                return;
        nfs_list_remove_request(req);
        cinfo->mds->ncommit--;
}
EXPORT_SYMBOL_GPL(nfs_request_remove_commit_list);

static void nfs_init_cinfo_from_inode(struct nfs_commit_info *cinfo,
                                      struct inode *inode)
{
        cinfo->inode = inode;
        cinfo->mds = &NFS_I(inode)->commit_info;
        cinfo->ds = pnfs_get_ds_info(inode);
        cinfo->dreq = NULL;
        cinfo->completion_ops = &nfs_commit_completion_ops;
}

void nfs_init_cinfo(struct nfs_commit_info *cinfo,
                    struct inode *inode,
                    struct nfs_direct_req *dreq)
{
        if (dreq)
                nfs_init_cinfo_from_dreq(cinfo, dreq);
        else
                nfs_init_cinfo_from_inode(cinfo, inode);
}
EXPORT_SYMBOL_GPL(nfs_init_cinfo);

/*
 * Add a request to the inode's commit list.
 */
void
nfs_mark_request_commit(struct nfs_page *req, struct pnfs_layout_segment *lseg,
                        struct nfs_commit_info *cinfo, u32 ds_commit_idx)
{
        if (pnfs_mark_request_commit(req, lseg, cinfo, ds_commit_idx))
                return;
        nfs_request_add_commit_list(req, cinfo);
}

static void
nfs_clear_page_commit(struct page *page)
{
        dec_node_page_state(page, NR_UNSTABLE_NFS);
        dec_wb_stat(&inode_to_bdi(page_file_mapping(page)->host)->wb,
                    WB_RECLAIMABLE);
}

/* Called holding inode (/cinfo) lock */
static void
nfs_clear_request_commit(struct nfs_page *req)
{
        if (test_bit(PG_CLEAN, &req->wb_flags)) {
                struct inode *inode = d_inode(req->wb_context->dentry);
                struct nfs_commit_info cinfo;

                nfs_init_cinfo_from_inode(&cinfo, inode);
                if (!pnfs_clear_request_commit(req, &cinfo)) {
                        nfs_request_remove_commit_list(req, &cinfo);
                }
                nfs_clear_page_commit(req->wb_page);
        }
}

int nfs_write_need_commit(struct nfs_pgio_header *hdr)
{
        if (hdr->verf.committed == NFS_DATA_SYNC)
                return hdr->lseg == NULL;
        return hdr->verf.committed != NFS_FILE_SYNC;
}

static void nfs_write_completion(struct nfs_pgio_header *hdr)
{
        struct nfs_commit_info cinfo;
        unsigned long bytes = 0;

        if (test_bit(NFS_IOHDR_REDO, &hdr->flags))
                goto out;
        nfs_init_cinfo_from_inode(&cinfo, hdr->inode);
        while (!list_empty(&hdr->pages)) {
                struct nfs_page *req = nfs_list_entry(hdr->pages.next);

                bytes += req->wb_bytes;
                nfs_list_remove_request(req);
                if (test_bit(NFS_IOHDR_ERROR, &hdr->flags) &&
                    (hdr->good_bytes < bytes)) {
                        nfs_set_pageerror(req->wb_page);
                        nfs_context_set_write_error(req->wb_context, hdr->error);
                        goto remove_req;
                }
                if (nfs_write_need_commit(hdr)) {
                        memcpy(&req->wb_verf, &hdr->verf.verifier, sizeof(req->wb_verf));
                        nfs_mark_request_commit(req, hdr->lseg, &cinfo,
                                hdr->pgio_mirror_idx);
                        goto next;
                }
remove_req:
                nfs_inode_remove_request(req);
next:
                nfs_unlock_request(req);
                nfs_end_page_writeback(req);
                nfs_release_request(req);
        }
out:
        hdr->release(hdr);
}

unsigned long
nfs_reqs_to_commit(struct nfs_commit_info *cinfo)
{
        return cinfo->mds->ncommit;
}

/* cinfo->inode->i_lock held by caller */
int
nfs_scan_commit_list(struct list_head *src, struct list_head *dst,
                     struct nfs_commit_info *cinfo, int max)
{
        struct nfs_page *req, *tmp;
        int ret = 0;

        list_for_each_entry_safe(req, tmp, src, wb_list) {
                if (!nfs_lock_request(req))
                        continue;
                kref_get(&req->wb_kref);
                if (cond_resched_lock(&cinfo->inode->i_lock))
                        list_safe_reset_next(req, tmp, wb_list);
                nfs_request_remove_commit_list(req, cinfo);
                nfs_list_add_request(req, dst);
                ret++;
                if ((ret == max) && !cinfo->dreq)
                        break;
        }
        return ret;
}

/*
 * nfs_scan_commit - Scan an inode for commit requests
 * @inode: NFS inode to scan
 * @dst: mds destination list
 * @cinfo: mds and ds lists of reqs ready to commit
 *
 * Moves requests from the inode's 'commit' request list.
 * The requests are *not* checked to ensure that they form a contiguous set.
 */
int
nfs_scan_commit(struct inode *inode, struct list_head *dst,
                struct nfs_commit_info *cinfo)
{
        int ret = 0;

        spin_lock(&cinfo->inode->i_lock);
        if (cinfo->mds->ncommit > 0) {
                const int max = INT_MAX;

                ret = nfs_scan_commit_list(&cinfo->mds->list, dst,
                                           cinfo, max);
                ret += pnfs_scan_commit_lists(inode, cinfo, max - ret);
        }
        spin_unlock(&cinfo->inode->i_lock);
        return ret;
}

/*
 * Search for an existing write request, and attempt to update
 * it to reflect a new dirty region on a given page.
 *
 * If the attempt fails, then the existing request is flushed out
 * to disk.
 */
static struct nfs_page *nfs_try_to_update_request(struct inode *inode,
                struct page *page,
                unsigned int offset,
                unsigned int bytes)
{
        struct nfs_page *req;
        unsigned int rqend;
        unsigned int end;
        int error;

        if (!PagePrivate(page))
                return NULL;

        end = offset + bytes;
        spin_lock(&inode->i_lock);

        for (;;) {
                req = nfs_page_find_head_request_locked(NFS_I(inode), page);
                if (req == NULL)
                        goto out_unlock;

                /* should be handled by nfs_flush_incompatible */
                WARN_ON_ONCE(req->wb_head != req);
                WARN_ON_ONCE(req->wb_this_page != req);

                rqend = req->wb_offset + req->wb_bytes;
                /*
                 * Tell the caller to flush out the request if
                 * the offsets are non-contiguous.
                 * Note: nfs_flush_incompatible() will already
                 * have flushed out requests having wrong owners.
                 */
                if (offset > rqend
                    || end < req->wb_offset)
                        goto out_flushme;

                if (nfs_lock_request(req))
                        break;

                /* The request is locked, so wait and then retry */
                spin_unlock(&inode->i_lock);
                error = nfs_wait_on_request(req);
                nfs_release_request(req);
                if (error != 0)
                        goto out_err;
                spin_lock(&inode->i_lock);
        }

        /* Okay, the request matches. Update the region */
        if (offset < req->wb_offset) {
                req->wb_offset = offset;
                req->wb_pgbase = offset;
        }
        if (end > rqend)
                req->wb_bytes = end - req->wb_offset;
        else
                req->wb_bytes = rqend - req->wb_offset;
out_unlock:
        if (req)
                nfs_clear_request_commit(req);
        spin_unlock(&inode->i_lock);
        return req;
out_flushme:
        spin_unlock(&inode->i_lock);
        nfs_release_request(req);
        error = nfs_wb_page(inode, page);
out_err:
        return ERR_PTR(error);
}

/*
 * Try to update an existing write request, or create one if there is none.
 *
 * Note: Should always be called with the Page Lock held to prevent races
 * if we have to add a new request. Also assumes that the caller has
 * already called nfs_flush_incompatible() if necessary.
 */
static struct nfs_page * nfs_setup_write_request(struct nfs_open_context* ctx,
                struct page *page, unsigned int offset, unsigned int bytes)
{
        struct inode *inode = page_file_mapping(page)->host;
        struct nfs_page *req;

        req = nfs_try_to_update_request(inode, page, offset, bytes);
        if (req != NULL)
                goto out;
        req = nfs_create_request(ctx, page, NULL, offset, bytes);
        if (IS_ERR(req))
                goto out;
        nfs_inode_add_request(inode, req);
out:
        return req;
}

static int nfs_writepage_setup(struct nfs_open_context *ctx, struct page *page,
                unsigned int offset, unsigned int count)
{
        struct nfs_page *req;

        req = nfs_setup_write_request(ctx, page, offset, count);
        if (IS_ERR(req))
                return PTR_ERR(req);
        /* Update file length */
        nfs_grow_file(page, offset, count);
        nfs_mark_uptodate(req);
        nfs_mark_request_dirty(req);
        nfs_unlock_and_release_request(req);
        return 0;
}

int nfs_flush_incompatible(struct file *file, struct page *page)
{
        struct nfs_open_context *ctx = nfs_file_open_context(file);
        struct nfs_lock_context *l_ctx;
        struct file_lock_context *flctx = file_inode(file)->i_flctx;
        struct nfs_page *req;
        int do_flush, status;
        /*
         * Look for a request corresponding to this page. If there
         * is one, and it belongs to another file, we flush it out
         * before we try to copy anything into the page. Do this
         * due to the lack of an ACCESS-type call in NFSv2.
         * Also do the same if we find a request from an existing
         * dropped page.
         */
        do {
                req = nfs_page_find_head_request(page);
                if (req == NULL)
                        return 0;
                l_ctx = req->wb_lock_context;
                do_flush = req->wb_page != page ||
                        !nfs_match_open_context(req->wb_context, ctx);
                /* for now, flush if more than 1 request in page_group */
                do_flush |= req->wb_this_page != req;
                if (l_ctx && flctx &&
                    !(list_empty_careful(&flctx->flc_posix) &&
                      list_empty_careful(&flctx->flc_flock))) {
                        do_flush |= l_ctx->lockowner != current->files;
                }
                nfs_release_request(req);
                if (!do_flush)
                        return 0;
                status = nfs_wb_page(page_file_mapping(page)->host, page);
        } while (status == 0);
        return status;
}

/*
 * Avoid buffered writes when a open context credential's key would
 * expire soon.
 *
 * Returns -EACCES if the key will expire within RPC_KEY_EXPIRE_FAIL.
 *
 * Return 0 and set a credential flag which triggers the inode to flush
 * and performs  NFS_FILE_SYNC writes if the key will expired within
 * RPC_KEY_EXPIRE_TIMEO.
 */
int
nfs_key_timeout_notify(struct file *filp, struct inode *inode)
{
        struct nfs_open_context *ctx = nfs_file_open_context(filp);
        struct rpc_auth *auth = NFS_SERVER(inode)->client->cl_auth;

        return rpcauth_key_timeout_notify(auth, ctx->cred);
}

/*
 * Test if the open context credential key is marked to expire soon.
 */
bool nfs_ctx_key_to_expire(struct nfs_open_context *ctx, struct inode *inode)
{
        struct rpc_auth *auth = NFS_SERVER(inode)->client->cl_auth;

        return rpcauth_cred_key_to_expire(auth, ctx->cred);
}

/*
 * If the page cache is marked as unsafe or invalid, then we can't rely on
 * the PageUptodate() flag. In this case, we will need to turn off
 * write optimisations that depend on the page contents being correct.
 */
static bool nfs_write_pageuptodate(struct page *page, struct inode *inode)
{
        struct nfs_inode *nfsi = NFS_I(inode);

        if (nfs_have_delegated_attributes(inode))
                goto out;
        if (nfsi->cache_validity & NFS_INO_REVAL_PAGECACHE)
                return false;
        smp_rmb();
        if (test_bit(NFS_INO_INVALIDATING, &nfsi->flags))
                return false;
out:
        if (nfsi->cache_validity & NFS_INO_INVALID_DATA)
                return false;
        return PageUptodate(page) != 0;
}

static bool
is_whole_file_wrlock(struct file_lock *fl)
{
        return fl->fl_start == 0 && fl->fl_end == OFFSET_MAX &&
                        fl->fl_type == F_WRLCK;
}

/* If we know the page is up to date, and we're not using byte range locks (or
 * if we have the whole file locked for writing), it may be more efficient to
 * extend the write to cover the entire page in order to avoid fragmentation
 * inefficiencies.
 *
 * If the file is opened for synchronous writes then we can just skip the rest
 * of the checks.
 */
static int nfs_can_extend_write(struct file *file, struct page *page, struct inode *inode)
{
        int ret;
        struct file_lock_context *flctx = inode->i_flctx;
        struct file_lock *fl;

        if (file->f_flags & O_DSYNC)
                return 0;
        if (!nfs_write_pageuptodate(page, inode))
                return 0;
        if (NFS_PROTO(inode)->have_delegation(inode, FMODE_WRITE))
                return 1;
        if (!flctx || (list_empty_careful(&flctx->flc_flock) &&
                       list_empty_careful(&flctx->flc_posix)))
                return 1;

        /* Check to see if there are whole file write locks */
        ret = 0;
        spin_lock(&flctx->flc_lock);
        if (!list_empty(&flctx->flc_posix)) {
                fl = list_first_entry(&flctx->flc_posix, struct file_lock,
                                        fl_list);
                if (is_whole_file_wrlock(fl))
                        ret = 1;
        } else if (!list_empty(&flctx->flc_flock)) {
                fl = list_first_entry(&flctx->flc_flock, struct file_lock,
                                        fl_list);
                if (fl->fl_type == F_WRLCK)
                        ret = 1;
        }
        spin_unlock(&flctx->flc_lock);
        return ret;
}

/*
 * Update and possibly write a cached page of an NFS file.
 *
 * XXX: Keep an eye on generic_file_read to make sure it doesn't do bad
 * things with a page scheduled for an RPC call (e.g. invalidate it).
 */
int nfs_updatepage(struct file *file, struct page *page,
                unsigned int offset, unsigned int count)
{
        struct nfs_open_context *ctx = nfs_file_open_context(file);
        struct inode    *inode = page_file_mapping(page)->host;
        int             status = 0;

        nfs_inc_stats(inode, NFSIOS_VFSUPDATEPAGE);

        dprintk("NFS:       nfs_updatepage(%pD2 %d@%lld)\n",
                file, count, (long long)(page_file_offset(page) + offset));

        if (!count)
                goto out;

        if (nfs_can_extend_write(file, page, inode)) {
                count = max(count + offset, nfs_page_length(page));
                offset = 0;
        }

        status = nfs_writepage_setup(ctx, page, offset, count);
        if (status < 0)
                nfs_set_pageerror(page);
        else
                __set_page_dirty_nobuffers(page);
out:
        dprintk("NFS:       nfs_updatepage returns %d (isize %lld)\n",
                        status, (long long)i_size_read(inode));
        return status;
}

static int flush_task_priority(int how)
{
        switch (how & (FLUSH_HIGHPRI|FLUSH_LOWPRI)) {
                case FLUSH_HIGHPRI:
                        return RPC_PRIORITY_HIGH;
                case FLUSH_LOWPRI:
                        return RPC_PRIORITY_LOW;
        }
        return RPC_PRIORITY_NORMAL;
}

static void nfs_initiate_write(struct nfs_pgio_header *hdr,
                               struct rpc_message *msg,
                               const struct nfs_rpc_ops *rpc_ops,
                               struct rpc_task_setup *task_setup_data, int how)
{
        int priority = flush_task_priority(how);

        task_setup_data->priority = priority;
        rpc_ops->write_setup(hdr, msg);

        nfs4_state_protect_write(NFS_SERVER(hdr->inode)->nfs_client,
                                 &task_setup_data->rpc_client, msg, hdr);
}

/* If a nfs_flush_* function fails, it should remove reqs from @head and
 * call this on each, which will prepare them to be retried on next
 * writeback using standard nfs.
 */
static void nfs_redirty_request(struct nfs_page *req)
{
        nfs_mark_request_dirty(req);
        set_bit(NFS_CONTEXT_RESEND_WRITES, &req->wb_context->flags);
        nfs_unlock_request(req);
        nfs_end_page_writeback(req);
        nfs_release_request(req);
}

static void nfs_async_write_error(struct list_head *head)
{
        struct nfs_page *req;

        while (!list_empty(head)) {
                req = nfs_list_entry(head->next);
                nfs_list_remove_request(req);
                nfs_redirty_request(req);
        }
}

static void nfs_async_write_reschedule_io(struct nfs_pgio_header *hdr)
{
        nfs_async_write_error(&hdr->pages);
}

static const struct nfs_pgio_completion_ops nfs_async_write_completion_ops = {
        .error_cleanup = nfs_async_write_error,
        .completion = nfs_write_completion,
        .reschedule_io = nfs_async_write_reschedule_io,
};

void nfs_pageio_init_write(struct nfs_pageio_descriptor *pgio,
                               struct inode *inode, int ioflags, bool force_mds,
                               const struct nfs_pgio_completion_ops *compl_ops)
{
        struct nfs_server *server = NFS_SERVER(inode);
        const struct nfs_pageio_ops *pg_ops = &nfs_pgio_rw_ops;

#ifdef CONFIG_NFS_V4_1
        if (server->pnfs_curr_ld && !force_mds)
                pg_ops = server->pnfs_curr_ld->pg_write_ops;
#endif
        nfs_pageio_init(pgio, inode, pg_ops, compl_ops, &nfs_rw_write_ops,
                        server->wsize, ioflags);
}
EXPORT_SYMBOL_GPL(nfs_pageio_init_write);

void nfs_pageio_reset_write_mds(struct nfs_pageio_descriptor *pgio)
{
        struct nfs_pgio_mirror *mirror;

        if (pgio->pg_ops && pgio->pg_ops->pg_cleanup)
                pgio->pg_ops->pg_cleanup(pgio);

        pgio->pg_ops = &nfs_pgio_rw_ops;

        nfs_pageio_stop_mirroring(pgio);

        mirror = &pgio->pg_mirrors[0];
        mirror->pg_bsize = NFS_SERVER(pgio->pg_inode)->wsize;
}
EXPORT_SYMBOL_GPL(nfs_pageio_reset_write_mds);


void nfs_commit_prepare(struct rpc_task *task, void *calldata)
{
        struct nfs_commit_data *data = calldata;

        NFS_PROTO(data->inode)->commit_rpc_prepare(task, data);
}

/*
 * Special version of should_remove_suid() that ignores capabilities.
 */
static int nfs_should_remove_suid(const struct inode *inode)
{
        umode_t mode = inode->i_mode;
        int kill = 0;

        /* suid always must be killed */
        if (unlikely(mode & S_ISUID))
                kill = ATTR_KILL_SUID;

        /*
         * sgid without any exec bits is just a mandatory locking mark; leave
         * it alone.  If some exec bits are set, it's a real sgid; kill it.
         */
        if (unlikely((mode & S_ISGID) && (mode & S_IXGRP)))
                kill |= ATTR_KILL_SGID;

        if (unlikely(kill && S_ISREG(mode)))
                return kill;

        return 0;
}

static void nfs_writeback_check_extend(struct nfs_pgio_header *hdr,
                struct nfs_fattr *fattr)
{
        struct nfs_pgio_args *argp = &hdr->args;
        struct nfs_pgio_res *resp = &hdr->res;
        u64 size = argp->offset + resp->count;

        if (!(fattr->valid & NFS_ATTR_FATTR_SIZE))
                fattr->size = size;
        if (nfs_size_to_loff_t(fattr->size) < i_size_read(hdr->inode)) {
                fattr->valid &= ~NFS_ATTR_FATTR_SIZE;
                return;
        }
        if (size != fattr->size)
                return;
        /* Set attribute barrier */
        nfs_fattr_set_barrier(fattr);
        /* ...and update size */
        fattr->valid |= NFS_ATTR_FATTR_SIZE;
}

void nfs_writeback_update_inode(struct nfs_pgio_header *hdr)
{
        struct nfs_fattr *fattr = &hdr->fattr;
        struct inode *inode = hdr->inode;

        spin_lock(&inode->i_lock);
        nfs_writeback_check_extend(hdr, fattr);
        nfs_post_op_update_inode_force_wcc_locked(inode, fattr);
        spin_unlock(&inode->i_lock);
}
EXPORT_SYMBOL_GPL(nfs_writeback_update_inode);

/*
 * This function is called when the WRITE call is complete.
 */
static int nfs_writeback_done(struct rpc_task *task,
                              struct nfs_pgio_header *hdr,
                              struct inode *inode)
{
        int status;

        /*
         * ->write_done will attempt to use post-op attributes to detect
         * conflicting writes by other clients.  A strict interpretation
         * of close-to-open would allow us to continue caching even if
         * another writer had changed the file, but some applications
         * depend on tighter cache coherency when writing.
         */
        status = NFS_PROTO(inode)->write_done(task, hdr);
        if (status != 0)
                return status;
        nfs_add_stats(inode, NFSIOS_SERVERWRITTENBYTES, hdr->res.count);

        if (hdr->res.verf->committed < hdr->args.stable &&
            task->tk_status >= 0) {
                /* We tried a write call, but the server did not
                 * commit data to stable storage even though we
                 * requested it.
                 * Note: There is a known bug in Tru64 < 5.0 in which
                 *       the server reports NFS_DATA_SYNC, but performs
                 *       NFS_FILE_SYNC. We therefore implement this checking
                 *       as a dprintk() in order to avoid filling syslog.
                 */
                static unsigned long    complain;

                /* Note this will print the MDS for a DS write */
                if (time_before(complain, jiffies)) {
                        dprintk("NFS:       faulty NFS server %s:"
                                " (committed = %d) != (stable = %d)\n",
                                NFS_SERVER(inode)->nfs_client->cl_hostname,
                                hdr->res.verf->committed, hdr->args.stable);
                        complain = jiffies + 300 * HZ;
                }
        }

        /* Deal with the suid/sgid bit corner case */
        if (nfs_should_remove_suid(inode))
                nfs_mark_for_revalidate(inode);
        return 0;
}

/*
 * This function is called when the WRITE call is complete.
 */
static void nfs_writeback_result(struct rpc_task *task,
                                 struct nfs_pgio_header *hdr)
{
        struct nfs_pgio_args    *argp = &hdr->args;
        struct nfs_pgio_res     *resp = &hdr->res;

        if (resp->count < argp->count) {
                static unsigned long    complain;

                /* This a short write! */
                nfs_inc_stats(hdr->inode, NFSIOS_SHORTWRITE);

                /* Has the server at least made some progress? */
                if (resp->count == 0) {
                        if (time_before(complain, jiffies)) {
                                printk(KERN_WARNING
                                       "NFS: Server wrote zero bytes, expected %u.\n",
                                       argp->count);
                                complain = jiffies + 300 * HZ;
                        }
                        nfs_set_pgio_error(hdr, -EIO, argp->offset);
                        task->tk_status = -EIO;
                        return;
                }

                /* For non rpc-based layout drivers, retry-through-MDS */
                if (!task->tk_ops) {
                        hdr->pnfs_error = -EAGAIN;
                        return;
                }

                /* Was this an NFSv2 write or an NFSv3 stable write? */
                if (resp->verf->committed != NFS_UNSTABLE) {
                        /* Resend from where the server left off */
                        hdr->mds_offset += resp->count;
                        argp->offset += resp->count;
                        argp->pgbase += resp->count;
                        argp->count -= resp->count;
                } else {
                        /* Resend as a stable write in order to avoid
                         * headaches in the case of a server crash.
                         */
                        argp->stable = NFS_FILE_SYNC;
                }
                rpc_restart_call_prepare(task);
        }
}

static int wait_on_commit(struct nfs_mds_commit_info *cinfo)
{
        return wait_on_atomic_t(&cinfo->rpcs_out,
                        nfs_wait_atomic_killable, TASK_KILLABLE);
}

static void nfs_commit_begin(struct nfs_mds_commit_info *cinfo)
{
        atomic_inc(&cinfo->rpcs_out);
}

static void nfs_commit_end(struct nfs_mds_commit_info *cinfo)
{
        if (atomic_dec_and_test(&cinfo->rpcs_out))
                wake_up_atomic_t(&cinfo->rpcs_out);
}

void nfs_commitdata_release(struct nfs_commit_data *data)
{
        put_nfs_open_context(data->context);
        nfs_commit_free(data);
}
EXPORT_SYMBOL_GPL(nfs_commitdata_release);

int nfs_initiate_commit(struct rpc_clnt *clnt, struct nfs_commit_data *data,
                        const struct nfs_rpc_ops *nfs_ops,
                        const struct rpc_call_ops *call_ops,
                        int how, int flags)
{
        struct rpc_task *task;
        int priority = flush_task_priority(how);
        struct rpc_message msg = {
                .rpc_argp = &data->args,
                .rpc_resp = &data->res,
                .rpc_cred = data->cred,
        };
        struct rpc_task_setup task_setup_data = {
                .task = &data->task,
                .rpc_client = clnt,
                .rpc_message = &msg,
                .callback_ops = call_ops,
                .callback_data = data,
                .workqueue = nfsiod_workqueue,
                .flags = RPC_TASK_ASYNC | flags,
                .priority = priority,
        };
        /* Set up the initial task struct.  */
        nfs_ops->commit_setup(data, &msg);

        dprintk("NFS: initiated commit call\n");

        nfs4_state_protect(NFS_SERVER(data->inode)->nfs_client,
                NFS_SP4_MACH_CRED_COMMIT, &task_setup_data.rpc_client, &msg);

        task = rpc_run_task(&task_setup_data);
        if (IS_ERR(task))
                return PTR_ERR(task);
        if (how & FLUSH_SYNC)
                rpc_wait_for_completion_task(task);
        rpc_put_task(task);
        return 0;
}
EXPORT_SYMBOL_GPL(nfs_initiate_commit);

static loff_t nfs_get_lwb(struct list_head *head)
{
        loff_t lwb = 0;
        struct nfs_page *req;

        list_for_each_entry(req, head, wb_list)
                if (lwb < (req_offset(req) + req->wb_bytes))
                        lwb = req_offset(req) + req->wb_bytes;

        return lwb;
}

/*
 * Set up the argument/result storage required for the RPC call.
 */
void nfs_init_commit(struct nfs_commit_data *data,
                     struct list_head *head,
                     struct pnfs_layout_segment *lseg,
                     struct nfs_commit_info *cinfo)
{
        struct nfs_page *first = nfs_list_entry(head->next);
        struct inode *inode = d_inode(first->wb_context->dentry);

        /* Set up the RPC argument and reply structs
         * NB: take care not to mess about with data->commit et al. */

        list_splice_init(head, &data->pages);

        data->inode       = inode;
        data->cred        = first->wb_context->cred;
        data->lseg        = lseg; /* reference transferred */
        /* only set lwb for pnfs commit */
        if (lseg)
                data->lwb = nfs_get_lwb(&data->pages);
        data->mds_ops     = &nfs_commit_ops;
        data->completion_ops = cinfo->completion_ops;
        data->dreq        = cinfo->dreq;

        data->args.fh     = NFS_FH(data->inode);
        /* Note: we always request a commit of the entire inode */
        data->args.offset = 0;
        data->args.count  = 0;
        data->context     = get_nfs_open_context(first->wb_context);
        data->res.fattr   = &data->fattr;
        data->res.verf    = &data->verf;
        nfs_fattr_init(&data->fattr);
}
EXPORT_SYMBOL_GPL(nfs_init_commit);

void nfs_retry_commit(struct list_head *page_list,
                      struct pnfs_layout_segment *lseg,
                      struct nfs_commit_info *cinfo,
                      u32 ds_commit_idx)
{
        struct nfs_page *req;

        while (!list_empty(page_list)) {
                req = nfs_list_entry(page_list->next);
                nfs_list_remove_request(req);
                nfs_mark_request_commit(req, lseg, cinfo, ds_commit_idx);
                if (!cinfo->dreq)
                        nfs_clear_page_commit(req->wb_page);
                nfs_unlock_and_release_request(req);
        }
}
EXPORT_SYMBOL_GPL(nfs_retry_commit);

static void
nfs_commit_resched_write(struct nfs_commit_info *cinfo,
                struct nfs_page *req)
{
        __set_page_dirty_nobuffers(req->wb_page);
}

/*
 * Commit dirty pages
 */
static int
nfs_commit_list(struct inode *inode, struct list_head *head, int how,
                struct nfs_commit_info *cinfo)
{
        struct nfs_commit_data  *data;

        /* another commit raced with us */
        if (list_empty(head))
                return 0;

        data = nfs_commitdata_alloc(true);

        /* Set up the argument struct */
        nfs_init_commit(data, head, NULL, cinfo);
        atomic_inc(&cinfo->mds->rpcs_out);
        return nfs_initiate_commit(NFS_CLIENT(inode), data, NFS_PROTO(inode),
                                   data->mds_ops, how, 0);
}

int nfs_commit_file(struct file *file, struct nfs_write_verifier *verf)
{
        struct inode *inode = file_inode(file);
        struct nfs_open_context *open;
        struct nfs_commit_info cinfo;
        struct nfs_page *req;
        int ret;

        open = get_nfs_open_context(nfs_file_open_context(file));
        req  = nfs_create_request(open, NULL, NULL, 0, i_size_read(inode));
        if (IS_ERR(req)) {
                ret = PTR_ERR(req);
                goto out_put;
        }

        nfs_init_cinfo_from_inode(&cinfo, inode);

        memcpy(&req->wb_verf, verf, sizeof(struct nfs_write_verifier));
        nfs_request_add_commit_list(req, &cinfo);
        ret = nfs_commit_inode(inode, FLUSH_SYNC);
        if (ret > 0)
                ret = 0;

        nfs_free_request(req);
out_put:
        put_nfs_open_context(open);
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_commit_file);

/*
 * COMMIT call returned
 */
static void nfs_commit_done(struct rpc_task *task, void *calldata)
{
        struct nfs_commit_data  *data = calldata;

        dprintk("NFS: %5u nfs_commit_done (status %d)\n",
                                task->tk_pid, task->tk_status);

        /* Call the NFS version-specific code */
        NFS_PROTO(data->inode)->commit_done(task, data);
}

static void nfs_commit_release_pages(struct nfs_commit_data *data)
{
        struct nfs_page *req;
        int status = data->task.tk_status;
        struct nfs_commit_info cinfo;
        struct nfs_server *nfss;

        while (!list_empty(&data->pages)) {
                req = nfs_list_entry(data->pages.next);
                nfs_list_remove_request(req);
                if (req->wb_page)
                        nfs_clear_page_commit(req->wb_page);

                dprintk("NFS:       commit (%s/%llu %d@%lld)",
                        req->wb_context->dentry->d_sb->s_id,
                        (unsigned long long)NFS_FILEID(d_inode(req->wb_context->dentry)),
                        req->wb_bytes,
                        (long long)req_offset(req));
                if (status < 0) {
                        nfs_context_set_write_error(req->wb_context, status);
                        if (req->wb_page)
                                nfs_inode_remove_request(req);
                        dprintk_cont(", error = %d\n", status);
                        goto next;
                }

                /* Okay, COMMIT succeeded, apparently. Check the verifier
                 * returned by the server against all stored verfs. */
                if (!nfs_write_verifier_cmp(&req->wb_verf, &data->verf.verifier)) {
                        /* We have a match */
                        if (req->wb_page)
                                nfs_inode_remove_request(req);
                        dprintk_cont(" OK\n");
                        goto next;
                }
                /* We have a mismatch. Write the page again */
                dprintk_cont(" mismatch\n");
                nfs_mark_request_dirty(req);
                set_bit(NFS_CONTEXT_RESEND_WRITES, &req->wb_context->flags);
        next:
                nfs_unlock_and_release_request(req);
        }
        nfss = NFS_SERVER(data->inode);
        if (atomic_long_read(&nfss->writeback) < NFS_CONGESTION_OFF_THRESH)
                clear_bdi_congested(&nfss->backing_dev_info, BLK_RW_ASYNC);

        nfs_init_cinfo(&cinfo, data->inode, data->dreq);
        nfs_commit_end(cinfo.mds);
}

static void nfs_commit_release(void *calldata)
{
        struct nfs_commit_data *data = calldata;

        data->completion_ops->completion(data);
        nfs_commitdata_release(calldata);
}

static const struct rpc_call_ops nfs_commit_ops = {
        .rpc_call_prepare = nfs_commit_prepare,
        .rpc_call_done = nfs_commit_done,
        .rpc_release = nfs_commit_release,
};

static const struct nfs_commit_completion_ops nfs_commit_completion_ops = {
        .completion = nfs_commit_release_pages,
        .resched_write = nfs_commit_resched_write,
};

int nfs_generic_commit_list(struct inode *inode, struct list_head *head,
                            int how, struct nfs_commit_info *cinfo)
{
        int status;

        status = pnfs_commit_list(inode, head, how, cinfo);
        if (status == PNFS_NOT_ATTEMPTED)
                status = nfs_commit_list(inode, head, how, cinfo);
        return status;
}

int nfs_commit_inode(struct inode *inode, int how)
{
        LIST_HEAD(head);
        struct nfs_commit_info cinfo;
        int may_wait = how & FLUSH_SYNC;
        int error = 0;
        int res;

        nfs_init_cinfo_from_inode(&cinfo, inode);
        nfs_commit_begin(cinfo.mds);
        res = nfs_scan_commit(inode, &head, &cinfo);
        if (res)
                error = nfs_generic_commit_list(inode, &head, how, &cinfo);
        nfs_commit_end(cinfo.mds);
        if (error < 0)
                goto out_error;
        if (!may_wait)
                goto out_mark_dirty;
        error = wait_on_commit(cinfo.mds);
        if (error < 0)
                return error;
        return res;
out_error:
        res = error;
        /* Note: If we exit without ensuring that the commit is complete,
         * we must mark the inode as dirty. Otherwise, future calls to
         * sync_inode() with the WB_SYNC_ALL flag set will fail to ensure
         * that the data is on the disk.
         */
out_mark_dirty:
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        return res;
}
EXPORT_SYMBOL_GPL(nfs_commit_inode);

int nfs_write_inode(struct inode *inode, struct writeback_control *wbc)
{
        struct nfs_inode *nfsi = NFS_I(inode);
        int flags = FLUSH_SYNC;
        int ret = 0;

        /* no commits means nothing needs to be done */
        if (!nfsi->commit_info.ncommit)
                return ret;

        if (wbc->sync_mode == WB_SYNC_NONE) {
                /* Don't commit yet if this is a non-blocking flush and there
                 * are a lot of outstanding writes for this mapping.
                 */
                if (nfsi->commit_info.ncommit <= (nfsi->nrequests >> 1))
                        goto out_mark_dirty;

                /* don't wait for the COMMIT response */
                flags = 0;
        }

        ret = nfs_commit_inode(inode, flags);
        if (ret >= 0) {
                if (wbc->sync_mode == WB_SYNC_NONE) {
                        if (ret < wbc->nr_to_write)
                                wbc->nr_to_write -= ret;
                        else
                                wbc->nr_to_write = 0;
                }
                return 0;
        }
out_mark_dirty:
        __mark_inode_dirty(inode, I_DIRTY_DATASYNC);
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_write_inode);

/*
 * Wrapper for filemap_write_and_wait_range()
 *
 * Needed for pNFS in order to ensure data becomes visible to the
 * client.
 */
int nfs_filemap_write_and_wait_range(struct address_space *mapping,
                loff_t lstart, loff_t lend)
{
        int ret;

        ret = filemap_write_and_wait_range(mapping, lstart, lend);
        if (ret == 0)
                ret = pnfs_sync_inode(mapping->host, true);
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_filemap_write_and_wait_range);

/*
 * flush the inode to disk.
 */
int nfs_wb_all(struct inode *inode)
{
        int ret;

        trace_nfs_writeback_inode_enter(inode);

        ret = filemap_write_and_wait(inode->i_mapping);
        if (ret)
                goto out;
        ret = nfs_commit_inode(inode, FLUSH_SYNC);
        if (ret < 0)
                goto out;
        pnfs_sync_inode(inode, true);
        ret = 0;

out:
        trace_nfs_writeback_inode_exit(inode, ret);
        return ret;
}
EXPORT_SYMBOL_GPL(nfs_wb_all);

int nfs_wb_page_cancel(struct inode *inode, struct page *page)
{
        struct nfs_page *req;
        int ret = 0;

        wait_on_page_writeback(page);

        /* blocking call to cancel all requests and join to a single (head)
         * request */
        req = nfs_lock_and_join_requests(page, false);

        if (IS_ERR(req)) {
                ret = PTR_ERR(req);
        } else if (req) {
                /* all requests from this page have been cancelled by
                 * nfs_lock_and_join_requests, so just remove the head
                 * request from the inode / page_private pointer and
                 * release it */
                nfs_inode_remove_request(req);
                nfs_unlock_and_release_request(req);
        }

        return ret;
}

/*
 * Write back all requests on one page - we do this before reading it.
 */
int nfs_wb_single_page(struct inode *inode, struct page *page, bool launder)
{
        loff_t range_start = page_file_offset(page);
        loff_t range_end = range_start + (loff_t)(PAGE_SIZE - 1);
        struct writeback_control wbc = {
                .sync_mode = WB_SYNC_ALL,
                .nr_to_write = 0,
                .range_start = range_start,
                .range_end = range_end,
        };
        int ret;

        trace_nfs_writeback_page_enter(inode);

        for (;;) {
                wait_on_page_writeback(page);
                if (clear_page_dirty_for_io(page)) {
                        ret = nfs_writepage_locked(page, &wbc, launder);
                        if (ret < 0)
                                goto out_error;
                        continue;
                }
                ret = 0;
                if (!PagePrivate(page))
                        break;
                ret = nfs_commit_inode(inode, FLUSH_SYNC);
                if (ret < 0)
                        goto out_error;
        }
out_error:
        trace_nfs_writeback_page_exit(inode, ret);
        return ret;
}

#ifdef CONFIG_MIGRATION
int nfs_migrate_page(struct address_space *mapping, struct page *newpage,
                struct page *page, enum migrate_mode mode)
{
        /*
         * If PagePrivate is set, then the page is currently associated with
         * an in-progress read or write request. Don't try to migrate it.
         *
         * FIXME: we could do this in principle, but we'll need a way to ensure
         *        that we can safely release the inode reference while holding
         *        the page lock.
         */
        if (PagePrivate(page))
                return -EBUSY;

        if (!nfs_fscache_release_page(page, GFP_KERNEL))
                return -EBUSY;

        return migrate_page(mapping, newpage, page, mode);
}
#endif

int __init nfs_init_writepagecache(void)
{
        nfs_wdata_cachep = kmem_cache_create("nfs_write_data",
                                             sizeof(struct nfs_pgio_header),
                                             0, SLAB_HWCACHE_ALIGN,
                                             NULL);
        if (nfs_wdata_cachep == NULL)
                return -ENOMEM;

        nfs_wdata_mempool = mempool_create_slab_pool(MIN_POOL_WRITE,
                                                     nfs_wdata_cachep);
        if (nfs_wdata_mempool == NULL)
                goto out_destroy_write_cache;

        nfs_cdata_cachep = kmem_cache_create("nfs_commit_data",
                                             sizeof(struct nfs_commit_data),
                                             0, SLAB_HWCACHE_ALIGN,
                                             NULL);
        if (nfs_cdata_cachep == NULL)
                goto out_destroy_write_mempool;

        nfs_commit_mempool = mempool_create_slab_pool(MIN_POOL_COMMIT,
                                                      nfs_cdata_cachep);
        if (nfs_commit_mempool == NULL)
                goto out_destroy_commit_cache;

        /*
         * NFS congestion size, scale with available memory.
         *
         *  64MB:    8192k
         * 128MB:   11585k
         * 256MB:   16384k
         * 512MB:   23170k
         *   1GB:   32768k
         *   2GB:   46340k
         *   4GB:   65536k
         *   8GB:   92681k
         *  16GB:  131072k
         *
         * This allows larger machines to have larger/more transfers.
         * Limit the default to 256M
         */
        nfs_congestion_kb = (16*int_sqrt(totalram_pages)) << (PAGE_SHIFT-10);
        if (nfs_congestion_kb > 256*1024)
                nfs_congestion_kb = 256*1024;

        return 0;

out_destroy_commit_cache:
        kmem_cache_destroy(nfs_cdata_cachep);
out_destroy_write_mempool:
        mempool_destroy(nfs_wdata_mempool);
out_destroy_write_cache:
        kmem_cache_destroy(nfs_wdata_cachep);
        return -ENOMEM;
}

void nfs_destroy_writepagecache(void)
{
        mempool_destroy(nfs_commit_mempool);
        kmem_cache_destroy(nfs_cdata_cachep);
        mempool_destroy(nfs_wdata_mempool);
        kmem_cache_destroy(nfs_wdata_cachep);
}

static const struct nfs_rw_ops nfs_rw_write_ops = {
        .rw_mode                = FMODE_WRITE,
        .rw_alloc_header        = nfs_writehdr_alloc,
        .rw_free_header         = nfs_writehdr_free,
        .rw_done                = nfs_writeback_done,
        .rw_result              = nfs_writeback_result,
        .rw_initiate            = nfs_initiate_write,
};