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blk-flush.c
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// 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_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;
if (rq->bio)
rq->__sector = rq->bio->bi_iter.bi_sector;
/* 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],
blk_time_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_add_tail(&rq->queuelist, pending);
break;
case REQ_FSEQ_DATA:
fq->flush_data_in_flight++;
spin_lock(&q->requeue_lock);
list_move(&rq->queuelist, &q->requeue_list);
spin_unlock(&q->requeue_lock);
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->queuelist);
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, queuelist) {
unsigned int seq = blk_flush_cur_seq(rq);
BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
list_del_init(&rq->queuelist);
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, queuelist);
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 (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;
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);
spin_lock(&q->requeue_lock);
list_add_tail(&flush_rq->queuelist, &q->flush_list);
spin_unlock(&q->requeue_lock);
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);
fq->flush_data_in_flight--;
/*
* May have been corrupted by rq->rq_next reuse, we need to
* re-initialize rq->queuelist before reusing it here.
*/
INIT_LIST_HEAD(&rq->queuelist);
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;
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;
struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
bool supports_fua = q->limits.features & BLK_FEAT_FUA;
unsigned int policy = 0;
/* FLUSH/FUA request must never be merged */
WARN_ON_ONCE(rq->bio != rq->biotail);
if (blk_rq_sectors(rq))
policy |= REQ_FSEQ_DATA;
/*
* Check which flushes we need to sequence for this operation.
*/
if (blk_queue_write_cache(q)) {
if (rq->cmd_flags & REQ_PREFLUSH)
policy |= REQ_FSEQ_PREFLUSH;
if ((rq->cmd_flags & REQ_FUA) && !supports_fua)
policy |= REQ_FSEQ_POSTFLUSH;
}
/*
* @policy now records what operations need to be done. Adjust
* REQ_PREFLUSH and FUA for the driver.
*/
rq->cmd_flags &= ~REQ_PREFLUSH;
if (!supports_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_PREFLUSH;
spin_lock_irq(&fq->mq_flush_lock);
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]);
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);