// 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 blk_mq_ctx *ctx) { return blk_mq_map_queue(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, const struct io_comp_batch *iob) { 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(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, const struct io_comp_batch *iob) { 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(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(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);
