| // 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); |
| spin_lock(&q->requeue_lock); |
| list_add(&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->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); |
| |
| 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); |
| 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); |