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![Jens Axboe](/assets/img/avatar_default.png)
refcount_t is not as expensive as it used to be, but it's still more expensive than the io_uring method of using atomic_t and just checking for potential over/underflow. This borrows that same implementation, which in turn is based on the mm implementation from Linus. Reviewed-by: Keith Busch <kbusch@kernel.org> Signed-off-by: Jens Axboe <axboe@kernel.dk>
532 lines
16 KiB
C
532 lines
16 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* Functions to sequence PREFLUSH and FUA writes.
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*
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* Copyright (C) 2011 Max Planck Institute for Gravitational Physics
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* Copyright (C) 2011 Tejun Heo <tj@kernel.org>
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*
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* REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
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* optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
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* properties and hardware capability.
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*
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* If a request doesn't have data, only REQ_PREFLUSH makes sense, which
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* indicates a simple flush request. If there is data, REQ_PREFLUSH indicates
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* that the device cache should be flushed before the data is executed, and
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* REQ_FUA means that the data must be on non-volatile media on request
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* completion.
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*
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* If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
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* difference. The requests are either completed immediately if there's no data
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* or executed as normal requests otherwise.
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*
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* If the device has writeback cache and supports FUA, REQ_PREFLUSH is
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* translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
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*
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* If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
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* is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
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*
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* The actual execution of flush is double buffered. Whenever a request
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* needs to execute PRE or POSTFLUSH, it queues at
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* fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
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* REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush
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* completes, all the requests which were pending are proceeded to the next
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* step. This allows arbitrary merging of different types of PREFLUSH/FUA
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* requests.
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*
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* Currently, the following conditions are used to determine when to issue
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* flush.
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*
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* C1. At any given time, only one flush shall be in progress. This makes
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* double buffering sufficient.
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*
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* C2. Flush is deferred if any request is executing DATA of its sequence.
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* This avoids issuing separate POSTFLUSHes for requests which shared
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* PREFLUSH.
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*
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* C3. The second condition is ignored if there is a request which has
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* waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
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* starvation in the unlikely case where there are continuous stream of
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* FUA (without PREFLUSH) requests.
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*
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* For devices which support FUA, it isn't clear whether C2 (and thus C3)
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* is beneficial.
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*
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* Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
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* Once while executing DATA and again after the whole sequence is
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* complete. The first completion updates the contained bio but doesn't
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* finish it so that the bio submitter is notified only after the whole
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* sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in
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* req_bio_endio().
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*
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* The above peculiarity requires that each PREFLUSH/FUA request has only one
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* bio attached to it, which is guaranteed as they aren't allowed to be
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* merged in the usual way.
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*/
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/bio.h>
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#include <linux/blkdev.h>
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#include <linux/gfp.h>
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#include <linux/blk-mq.h>
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#include <linux/part_stat.h>
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#include "blk.h"
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#include "blk-mq.h"
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#include "blk-mq-tag.h"
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#include "blk-mq-sched.h"
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/* PREFLUSH/FUA sequences */
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enum {
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REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
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REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
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REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
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REQ_FSEQ_DONE = (1 << 3),
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REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
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REQ_FSEQ_POSTFLUSH,
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/*
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* If flush has been pending longer than the following timeout,
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* it's issued even if flush_data requests are still in flight.
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*/
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FLUSH_PENDING_TIMEOUT = 5 * HZ,
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};
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static void blk_kick_flush(struct request_queue *q,
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struct blk_flush_queue *fq, unsigned int flags);
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static inline struct blk_flush_queue *
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blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
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{
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return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
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}
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static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
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{
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unsigned int policy = 0;
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if (blk_rq_sectors(rq))
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policy |= REQ_FSEQ_DATA;
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if (fflags & (1UL << QUEUE_FLAG_WC)) {
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if (rq->cmd_flags & REQ_PREFLUSH)
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policy |= REQ_FSEQ_PREFLUSH;
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if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
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(rq->cmd_flags & REQ_FUA))
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policy |= REQ_FSEQ_POSTFLUSH;
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}
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return policy;
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}
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static unsigned int blk_flush_cur_seq(struct request *rq)
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{
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return 1 << ffz(rq->flush.seq);
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}
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static void blk_flush_restore_request(struct request *rq)
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{
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/*
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* After flush data completion, @rq->bio is %NULL but we need to
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* complete the bio again. @rq->biotail is guaranteed to equal the
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* original @rq->bio. Restore it.
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*/
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rq->bio = rq->biotail;
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/* make @rq a normal request */
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rq->rq_flags &= ~RQF_FLUSH_SEQ;
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rq->end_io = rq->flush.saved_end_io;
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}
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static void blk_flush_queue_rq(struct request *rq, bool add_front)
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{
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blk_mq_add_to_requeue_list(rq, add_front, true);
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}
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static void blk_account_io_flush(struct request *rq)
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{
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struct block_device *part = rq->q->disk->part0;
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part_stat_lock();
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part_stat_inc(part, ios[STAT_FLUSH]);
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part_stat_add(part, nsecs[STAT_FLUSH],
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ktime_get_ns() - rq->start_time_ns);
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part_stat_unlock();
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}
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/**
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* blk_flush_complete_seq - complete flush sequence
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* @rq: PREFLUSH/FUA request being sequenced
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* @fq: flush queue
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* @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
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* @error: whether an error occurred
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*
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* @rq just completed @seq part of its flush sequence, record the
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* completion and trigger the next step.
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*
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* CONTEXT:
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* spin_lock_irq(fq->mq_flush_lock)
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*/
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static void blk_flush_complete_seq(struct request *rq,
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struct blk_flush_queue *fq,
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unsigned int seq, blk_status_t error)
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{
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struct request_queue *q = rq->q;
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struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
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unsigned int cmd_flags;
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BUG_ON(rq->flush.seq & seq);
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rq->flush.seq |= seq;
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cmd_flags = rq->cmd_flags;
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if (likely(!error))
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seq = blk_flush_cur_seq(rq);
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else
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seq = REQ_FSEQ_DONE;
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switch (seq) {
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case REQ_FSEQ_PREFLUSH:
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case REQ_FSEQ_POSTFLUSH:
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/* queue for flush */
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if (list_empty(pending))
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fq->flush_pending_since = jiffies;
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list_move_tail(&rq->flush.list, pending);
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break;
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case REQ_FSEQ_DATA:
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list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
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blk_flush_queue_rq(rq, true);
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break;
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case REQ_FSEQ_DONE:
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/*
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* @rq was previously adjusted by blk_insert_flush() for
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* flush sequencing and may already have gone through the
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* flush data request completion path. Restore @rq for
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* normal completion and end it.
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*/
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BUG_ON(!list_empty(&rq->queuelist));
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list_del_init(&rq->flush.list);
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blk_flush_restore_request(rq);
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blk_mq_end_request(rq, error);
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break;
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default:
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BUG();
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}
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blk_kick_flush(q, fq, cmd_flags);
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}
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static void flush_end_io(struct request *flush_rq, blk_status_t error)
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{
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struct request_queue *q = flush_rq->q;
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struct list_head *running;
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struct request *rq, *n;
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unsigned long flags = 0;
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struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
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/* release the tag's ownership to the req cloned from */
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spin_lock_irqsave(&fq->mq_flush_lock, flags);
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if (!req_ref_put_and_test(flush_rq)) {
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fq->rq_status = error;
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spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
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return;
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}
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blk_account_io_flush(flush_rq);
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/*
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* Flush request has to be marked as IDLE when it is really ended
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* because its .end_io() is called from timeout code path too for
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* avoiding use-after-free.
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*/
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WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
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if (fq->rq_status != BLK_STS_OK) {
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error = fq->rq_status;
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fq->rq_status = BLK_STS_OK;
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}
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if (!q->elevator) {
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flush_rq->tag = BLK_MQ_NO_TAG;
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} else {
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blk_mq_put_driver_tag(flush_rq);
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flush_rq->internal_tag = BLK_MQ_NO_TAG;
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}
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running = &fq->flush_queue[fq->flush_running_idx];
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BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
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/* account completion of the flush request */
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fq->flush_running_idx ^= 1;
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/* and push the waiting requests to the next stage */
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list_for_each_entry_safe(rq, n, running, flush.list) {
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unsigned int seq = blk_flush_cur_seq(rq);
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BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
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blk_flush_complete_seq(rq, fq, seq, error);
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}
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spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
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}
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bool is_flush_rq(struct request *rq)
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{
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return rq->end_io == flush_end_io;
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}
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/**
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* blk_kick_flush - consider issuing flush request
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* @q: request_queue being kicked
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* @fq: flush queue
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* @flags: cmd_flags of the original request
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*
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* Flush related states of @q have changed, consider issuing flush request.
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* Please read the comment at the top of this file for more info.
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*
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* CONTEXT:
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* spin_lock_irq(fq->mq_flush_lock)
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*
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*/
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static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
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unsigned int flags)
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{
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struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
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struct request *first_rq =
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list_first_entry(pending, struct request, flush.list);
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struct request *flush_rq = fq->flush_rq;
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/* C1 described at the top of this file */
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if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
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return;
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/* C2 and C3 */
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if (!list_empty(&fq->flush_data_in_flight) &&
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time_before(jiffies,
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fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
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return;
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/*
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* Issue flush and toggle pending_idx. This makes pending_idx
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* different from running_idx, which means flush is in flight.
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*/
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fq->flush_pending_idx ^= 1;
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blk_rq_init(q, flush_rq);
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/*
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* In case of none scheduler, borrow tag from the first request
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* since they can't be in flight at the same time. And acquire
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* the tag's ownership for flush req.
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*
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* In case of IO scheduler, flush rq need to borrow scheduler tag
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* just for cheating put/get driver tag.
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*/
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flush_rq->mq_ctx = first_rq->mq_ctx;
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flush_rq->mq_hctx = first_rq->mq_hctx;
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if (!q->elevator) {
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flush_rq->tag = first_rq->tag;
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/*
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* We borrow data request's driver tag, so have to mark
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* this flush request as INFLIGHT for avoiding double
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* account of this driver tag
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*/
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flush_rq->rq_flags |= RQF_MQ_INFLIGHT;
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} else
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flush_rq->internal_tag = first_rq->internal_tag;
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flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
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flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
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flush_rq->rq_flags |= RQF_FLUSH_SEQ;
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flush_rq->end_io = flush_end_io;
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/*
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* Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
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* implied in refcount_inc_not_zero() called from
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* blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
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* and READ flush_rq->end_io
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*/
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smp_wmb();
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req_ref_set(flush_rq, 1);
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blk_flush_queue_rq(flush_rq, false);
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}
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static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
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{
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struct request_queue *q = rq->q;
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struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
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struct blk_mq_ctx *ctx = rq->mq_ctx;
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unsigned long flags;
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struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
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if (q->elevator) {
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WARN_ON(rq->tag < 0);
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blk_mq_put_driver_tag(rq);
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}
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/*
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* After populating an empty queue, kick it to avoid stall. Read
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* the comment in flush_end_io().
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*/
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spin_lock_irqsave(&fq->mq_flush_lock, flags);
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blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
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spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
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blk_mq_sched_restart(hctx);
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}
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/**
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* blk_insert_flush - insert a new PREFLUSH/FUA request
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* @rq: request to insert
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*
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* To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
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* or __blk_mq_run_hw_queue() to dispatch request.
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* @rq is being submitted. Analyze what needs to be done and put it on the
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* right queue.
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*/
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void blk_insert_flush(struct request *rq)
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{
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struct request_queue *q = rq->q;
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unsigned long fflags = q->queue_flags; /* may change, cache */
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unsigned int policy = blk_flush_policy(fflags, rq);
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struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
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/*
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* @policy now records what operations need to be done. Adjust
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* REQ_PREFLUSH and FUA for the driver.
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*/
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rq->cmd_flags &= ~REQ_PREFLUSH;
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if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
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rq->cmd_flags &= ~REQ_FUA;
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/*
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* REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
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* of those flags, we have to set REQ_SYNC to avoid skewing
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* the request accounting.
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*/
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rq->cmd_flags |= REQ_SYNC;
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/*
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* An empty flush handed down from a stacking driver may
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* translate into nothing if the underlying device does not
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* advertise a write-back cache. In this case, simply
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* complete the request.
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*/
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if (!policy) {
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blk_mq_end_request(rq, 0);
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return;
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}
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BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
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/*
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* If there's data but flush is not necessary, the request can be
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* processed directly without going through flush machinery. Queue
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* for normal execution.
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*/
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if ((policy & REQ_FSEQ_DATA) &&
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!(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
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blk_mq_request_bypass_insert(rq, false, true);
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return;
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}
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/*
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* @rq should go through flush machinery. Mark it part of flush
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* sequence and submit for further processing.
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*/
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memset(&rq->flush, 0, sizeof(rq->flush));
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INIT_LIST_HEAD(&rq->flush.list);
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rq->rq_flags |= RQF_FLUSH_SEQ;
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rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
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rq->end_io = mq_flush_data_end_io;
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spin_lock_irq(&fq->mq_flush_lock);
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blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
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spin_unlock_irq(&fq->mq_flush_lock);
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}
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/**
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* blkdev_issue_flush - queue a flush
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* @bdev: blockdev to issue flush for
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*
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* Description:
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* Issue a flush for the block device in question.
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*/
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int blkdev_issue_flush(struct block_device *bdev)
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{
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struct bio bio;
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bio_init(&bio, NULL, 0);
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bio_set_dev(&bio, bdev);
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bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
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return submit_bio_wait(&bio);
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}
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EXPORT_SYMBOL(blkdev_issue_flush);
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struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
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gfp_t flags)
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{
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struct blk_flush_queue *fq;
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int rq_sz = sizeof(struct request);
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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);
|