[linux-block.git] / block / blk-flush.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Functions to sequence PREFLUSH and FUA writes.
 *
 * Copyright (C) 2011           Max Planck Institute for Gravitational Physics
 * Copyright (C) 2011           Tejun Heo <tj@kernel.org>
 *
 * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
 * properties and hardware capability.
 *
 * If a request doesn't have data, only REQ_PREFLUSH makes sense, which
 * indicates a simple flush request.  If there is data, REQ_PREFLUSH indicates
 * that the device cache should be flushed before the data is executed, and
 * REQ_FUA means that the data must be on non-volatile media on request
 * completion.
 *
 * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
 * difference.  The requests are either completed immediately if there's no data
 * or executed as normal requests otherwise.
 *
 * If the device has writeback cache and supports FUA, REQ_PREFLUSH is
 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
 *
 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
 *
 * The actual execution of flush is double buffered.  Whenever a request
 * needs to execute PRE or POSTFLUSH, it queues at
 * fq->flush_queue[fq->flush_pending_idx].  Once certain criteria are met, a
 * REQ_OP_FLUSH is issued and the pending_idx is toggled.  When the flush
 * completes, all the requests which were pending are proceeded to the next
 * step.  This allows arbitrary merging of different types of PREFLUSH/FUA
 * requests.
 *
 * Currently, the following conditions are used to determine when to issue
 * flush.
 *
 * C1. At any given time, only one flush shall be in progress.  This makes
 *     double buffering sufficient.
 *
 * C2. Flush is deferred if any request is executing DATA of its sequence.
 *     This avoids issuing separate POSTFLUSHes for requests which shared
 *     PREFLUSH.
 *
 * C3. The second condition is ignored if there is a request which has
 *     waited longer than FLUSH_PENDING_TIMEOUT.  This is to avoid
 *     starvation in the unlikely case where there are continuous stream of
 *     FUA (without PREFLUSH) requests.
 *
 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
 * is beneficial.
 *
 * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
 * Once while executing DATA and again after the whole sequence is
 * complete.  The first completion updates the contained bio but doesn't
 * finish it so that the bio submitter is notified only after the whole
 * sequence is complete.  This is implemented by testing RQF_FLUSH_SEQ in
 * req_bio_endio().
 *
 * The above peculiarity requires that each PREFLUSH/FUA request has only one
 * bio attached to it, which is guaranteed as they aren't allowed to be
 * merged in the usual way.
 */

#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/bio.h>
#include <linux/blkdev.h>
#include <linux/gfp.h>
#include <linux/part_stat.h>

#include "blk.h"
#include "blk-mq.h"
#include "blk-mq-sched.h"

/* PREFLUSH/FUA sequences */
enum {
        REQ_FSEQ_PREFLUSH       = (1 << 0), /* pre-flushing in progress */
        REQ_FSEQ_DATA           = (1 << 1), /* data write in progress */
        REQ_FSEQ_POSTFLUSH      = (1 << 2), /* post-flushing in progress */
        REQ_FSEQ_DONE           = (1 << 3),

        REQ_FSEQ_ACTIONS        = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
                                  REQ_FSEQ_POSTFLUSH,

        /*
         * If flush has been pending longer than the following timeout,
         * it's issued even if flush_data requests are still in flight.
         */
        FLUSH_PENDING_TIMEOUT   = 5 * HZ,
};

static void blk_kick_flush(struct request_queue *q,
                           struct blk_flush_queue *fq, blk_opf_t flags);

static inline struct blk_flush_queue *
blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
{
        return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
}

static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
{
        unsigned int policy = 0;

        if (blk_rq_sectors(rq))
                policy |= REQ_FSEQ_DATA;

        if (fflags & (1UL << QUEUE_FLAG_WC)) {
                if (rq->cmd_flags & REQ_PREFLUSH)
                        policy |= REQ_FSEQ_PREFLUSH;
                if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
                    (rq->cmd_flags & REQ_FUA))
                        policy |= REQ_FSEQ_POSTFLUSH;
        }
        return policy;
}

static unsigned int blk_flush_cur_seq(struct request *rq)
{
        return 1 << ffz(rq->flush.seq);
}

static void blk_flush_restore_request(struct request *rq)
{
        /*
         * After flush data completion, @rq->bio is %NULL but we need to
         * complete the bio again.  @rq->biotail is guaranteed to equal the
         * original @rq->bio.  Restore it.
         */
        rq->bio = rq->biotail;

        /* make @rq a normal request */
        rq->rq_flags &= ~RQF_FLUSH_SEQ;
        rq->end_io = rq->flush.saved_end_io;
}

static void blk_account_io_flush(struct request *rq)
{
        struct block_device *part = rq->q->disk->part0;

        part_stat_lock();
        part_stat_inc(part, ios[STAT_FLUSH]);
        part_stat_add(part, nsecs[STAT_FLUSH],
                      ktime_get_ns() - rq->start_time_ns);
        part_stat_unlock();
}

/**
 * blk_flush_complete_seq - complete flush sequence
 * @rq: PREFLUSH/FUA request being sequenced
 * @fq: flush queue
 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
 * @error: whether an error occurred
 *
 * @rq just completed @seq part of its flush sequence, record the
 * completion and trigger the next step.
 *
 * CONTEXT:
 * spin_lock_irq(fq->mq_flush_lock)
 */
static void blk_flush_complete_seq(struct request *rq,
                                   struct blk_flush_queue *fq,
                                   unsigned int seq, blk_status_t error)
{
        struct request_queue *q = rq->q;
        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
        blk_opf_t cmd_flags;

        BUG_ON(rq->flush.seq & seq);
        rq->flush.seq |= seq;
        cmd_flags = rq->cmd_flags;

        if (likely(!error))
                seq = blk_flush_cur_seq(rq);
        else
                seq = REQ_FSEQ_DONE;

        switch (seq) {
        case REQ_FSEQ_PREFLUSH:
        case REQ_FSEQ_POSTFLUSH:
                /* queue for flush */
                if (list_empty(pending))
                        fq->flush_pending_since = jiffies;
                list_move_tail(&rq->flush.list, pending);
                break;

        case REQ_FSEQ_DATA:
                list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
                blk_mq_add_to_requeue_list(rq, 0);
                blk_mq_kick_requeue_list(q);
                break;

        case REQ_FSEQ_DONE:
                /*
                 * @rq was previously adjusted by blk_insert_flush() for
                 * flush sequencing and may already have gone through the
                 * flush data request completion path.  Restore @rq for
                 * normal completion and end it.
                 */
                list_del_init(&rq->flush.list);
                blk_flush_restore_request(rq);
                blk_mq_end_request(rq, error);
                break;

        default:
                BUG();
        }

        blk_kick_flush(q, fq, cmd_flags);
}

static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
                                       blk_status_t error)
{
        struct request_queue *q = flush_rq->q;
        struct list_head *running;
        struct request *rq, *n;
        unsigned long flags = 0;
        struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);

        /* release the tag's ownership to the req cloned from */
        spin_lock_irqsave(&fq->mq_flush_lock, flags);

        if (!req_ref_put_and_test(flush_rq)) {
                fq->rq_status = error;
                spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
                return RQ_END_IO_NONE;
        }

        blk_account_io_flush(flush_rq);
        /*
         * Flush request has to be marked as IDLE when it is really ended
         * because its .end_io() is called from timeout code path too for
         * avoiding use-after-free.
         */
        WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
        if (fq->rq_status != BLK_STS_OK) {
                error = fq->rq_status;
                fq->rq_status = BLK_STS_OK;
        }

        if (!q->elevator) {
                flush_rq->tag = BLK_MQ_NO_TAG;
        } else {
                blk_mq_put_driver_tag(flush_rq);
                flush_rq->internal_tag = BLK_MQ_NO_TAG;
        }

        running = &fq->flush_queue[fq->flush_running_idx];
        BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);

        /* account completion of the flush request */
        fq->flush_running_idx ^= 1;

        /* and push the waiting requests to the next stage */
        list_for_each_entry_safe(rq, n, running, flush.list) {
                unsigned int seq = blk_flush_cur_seq(rq);

                BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
                blk_flush_complete_seq(rq, fq, seq, error);
        }

        spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
        return RQ_END_IO_NONE;
}

bool is_flush_rq(struct request *rq)
{
        return rq->end_io == flush_end_io;
}

/**
 * blk_kick_flush - consider issuing flush request
 * @q: request_queue being kicked
 * @fq: flush queue
 * @flags: cmd_flags of the original request
 *
 * Flush related states of @q have changed, consider issuing flush request.
 * Please read the comment at the top of this file for more info.
 *
 * CONTEXT:
 * spin_lock_irq(fq->mq_flush_lock)
 *
 */
static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
                           blk_opf_t flags)
{
        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
        struct request *first_rq =
                list_first_entry(pending, struct request, flush.list);
        struct request *flush_rq = fq->flush_rq;

        /* C1 described at the top of this file */
        if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
                return;

        /* C2 and C3 */
        if (!list_empty(&fq->flush_data_in_flight) &&
            time_before(jiffies,
                        fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
                return;

        /*
         * Issue flush and toggle pending_idx.  This makes pending_idx
         * different from running_idx, which means flush is in flight.
         */
        fq->flush_pending_idx ^= 1;

        blk_rq_init(q, flush_rq);

        /*
         * In case of none scheduler, borrow tag from the first request
         * since they can't be in flight at the same time. And acquire
         * the tag's ownership for flush req.
         *
         * In case of IO scheduler, flush rq need to borrow scheduler tag
         * just for cheating put/get driver tag.
         */
        flush_rq->mq_ctx = first_rq->mq_ctx;
        flush_rq->mq_hctx = first_rq->mq_hctx;

        if (!q->elevator) {
                flush_rq->tag = first_rq->tag;

                /*
                 * We borrow data request's driver tag, so have to mark
                 * this flush request as INFLIGHT for avoiding double
                 * account of this driver tag
                 */
                flush_rq->rq_flags |= RQF_MQ_INFLIGHT;
        } else
                flush_rq->internal_tag = first_rq->internal_tag;

        flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
        flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
        flush_rq->rq_flags |= RQF_FLUSH_SEQ;
        flush_rq->end_io = flush_end_io;
        /*
         * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
         * implied in refcount_inc_not_zero() called from
         * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
         * and READ flush_rq->end_io
         */
        smp_wmb();
        req_ref_set(flush_rq, 1);

        blk_mq_add_to_requeue_list(flush_rq, 0);
        blk_mq_kick_requeue_list(q);
}

static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
                                               blk_status_t error)
{
        struct request_queue *q = rq->q;
        struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
        struct blk_mq_ctx *ctx = rq->mq_ctx;
        unsigned long flags;
        struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);

        if (q->elevator) {
                WARN_ON(rq->tag < 0);
                blk_mq_put_driver_tag(rq);
        }

        /*
         * After populating an empty queue, kick it to avoid stall.  Read
         * the comment in flush_end_io().
         */
        spin_lock_irqsave(&fq->mq_flush_lock, flags);
        blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
        spin_unlock_irqrestore(&fq->mq_flush_lock, flags);

        blk_mq_sched_restart(hctx);
        return RQ_END_IO_NONE;
}

static void blk_rq_init_flush(struct request *rq)
{
        rq->flush.seq = 0;
        INIT_LIST_HEAD(&rq->flush.list);
        rq->rq_flags |= RQF_FLUSH_SEQ;
        rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
        rq->end_io = mq_flush_data_end_io;
}

/*
 * Insert a PREFLUSH/FUA request into the flush state machine.
 * Returns true if the request has been consumed by the flush state machine,
 * or false if the caller should continue to process it.
 */
bool blk_insert_flush(struct request *rq)
{
        struct request_queue *q = rq->q;
        unsigned long fflags = q->queue_flags;  /* may change, cache */
        unsigned int policy = blk_flush_policy(fflags, rq);
        struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);

        /* FLUSH/FUA request must never be merged */
        WARN_ON_ONCE(rq->bio != rq->biotail);

        /*
         * @policy now records what operations need to be done.  Adjust
         * REQ_PREFLUSH and FUA for the driver.
         */
        rq->cmd_flags &= ~REQ_PREFLUSH;
        if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
                rq->cmd_flags &= ~REQ_FUA;

        /*
         * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
         * of those flags, we have to set REQ_SYNC to avoid skewing
         * the request accounting.
         */
        rq->cmd_flags |= REQ_SYNC;

        switch (policy) {
        case 0:
                /*
                 * An empty flush handed down from a stacking driver may
                 * translate into nothing if the underlying device does not
                 * advertise a write-back cache.  In this case, simply
                 * complete the request.
                 */
                blk_mq_end_request(rq, 0);
                return true;
        case REQ_FSEQ_DATA:
                /*
                 * If there's data, but no flush is necessary, the request can
                 * be processed directly without going through flush machinery.
                 * Queue for normal execution.
                 */
                return false;
        case REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH:
                /*
                 * Initialize the flush fields and completion handler to trigger
                 * the post flush, and then just pass the command on.
                 */
                blk_rq_init_flush(rq);
                rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
                spin_lock_irq(&fq->mq_flush_lock);
                list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
                spin_unlock_irq(&fq->mq_flush_lock);
                return false;
        default:
                /*
                 * Mark the request as part of a flush sequence and submit it
                 * for further processing to the flush state machine.
                 */
                blk_rq_init_flush(rq);
                spin_lock_irq(&fq->mq_flush_lock);
                blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
                spin_unlock_irq(&fq->mq_flush_lock);
                return true;
        }
}

/**
 * blkdev_issue_flush - queue a flush
 * @bdev:       blockdev to issue flush for
 *
 * Description:
 *    Issue a flush for the block device in question.
 */
int blkdev_issue_flush(struct block_device *bdev)
{
        struct bio bio;

        bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);
        return submit_bio_wait(&bio);
}
EXPORT_SYMBOL(blkdev_issue_flush);

struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
                                              gfp_t flags)
{
        struct blk_flush_queue *fq;
        int rq_sz = sizeof(struct request);

        fq = kzalloc_node(sizeof(*fq), flags, node);
        if (!fq)
                goto fail;

        spin_lock_init(&fq->mq_flush_lock);

        rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
        fq->flush_rq = kzalloc_node(rq_sz, flags, node);
        if (!fq->flush_rq)
                goto fail_rq;

        INIT_LIST_HEAD(&fq->flush_queue[0]);
        INIT_LIST_HEAD(&fq->flush_queue[1]);
        INIT_LIST_HEAD(&fq->flush_data_in_flight);

        return fq;

 fail_rq:
        kfree(fq);
 fail:
        return NULL;
}

void blk_free_flush_queue(struct blk_flush_queue *fq)
{
        /* bio based request queue hasn't flush queue */
        if (!fq)
                return;

        kfree(fq->flush_rq);
        kfree(fq);
}

/*
 * Allow driver to set its own lock class to fq->mq_flush_lock for
 * avoiding lockdep complaint.
 *
 * flush_end_io() may be called recursively from some driver, such as
 * nvme-loop, so lockdep may complain 'possible recursive locking' because
 * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
 * key. We need to assign different lock class for these driver's
 * fq->mq_flush_lock for avoiding the lockdep warning.
 *
 * Use dynamically allocated lock class key for each 'blk_flush_queue'
 * instance is over-kill, and more worse it introduces horrible boot delay
 * issue because synchronize_rcu() is implied in lockdep_unregister_key which
 * is called for each hctx release. SCSI probing may synchronously create and
 * destroy lots of MQ request_queues for non-existent devices, and some robot
 * test kernel always enable lockdep option. It is observed that more than half
 * an hour is taken during SCSI MQ probe with per-fq lock class.
 */
void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
                struct lock_class_key *key)
{
        lockdep_set_class(&hctx->fq->mq_flush_lock, key);
}
EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);