diff options
Diffstat (limited to 'block/blk-flush.c')
| -rw-r--r-- | block/blk-flush.c | 546 |
1 files changed, 546 insertions, 0 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c new file mode 100644 index 000000000..e73dc22d0 --- /dev/null +++ b/block/blk-flush.c @@ -0,0 +1,546 @@ +// 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->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); + 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; + + /* + * 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); + 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; + 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_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); |