diff options
Diffstat (limited to 'block/blk-flush.c')
| -rw-r--r-- | block/blk-flush.c | 529 |
1 files changed, 529 insertions, 0 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c new file mode 100644 index 000000000..20badd7b9 --- /dev/null +++ b/block/blk-flush.c @@ -0,0 +1,529 @@ +/* + * Functions to sequence FLUSH and FUA writes. + * + * Copyright (C) 2011 Max Planck Institute for Gravitational Physics + * Copyright (C) 2011 Tejun Heo <tj@kernel.org> + * + * This file is released under the GPLv2. + * + * REQ_{FLUSH|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_FLUSH makes sense, which + * indicates a simple flush request. If there is data, REQ_FLUSH 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, FLUSH 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_FLUSH 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_FLUSH 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 + * 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 FLUSH/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 FLUSH) requests. + * + * For devices which support FUA, it isn't clear whether C2 (and thus C3) + * is beneficial. + * + * Note that a sequenced FLUSH/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 REQ_FLUSH_SEQ in + * req_bio_endio(). + * + * The above peculiarity requires that each FLUSH/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/blk-mq.h> + +#include "blk.h" +#include "blk-mq.h" + +/* FLUSH/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 bool blk_kick_flush(struct request_queue *q, + struct blk_flush_queue *fq); + +static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq) +{ + unsigned int policy = 0; + + if (blk_rq_sectors(rq)) + policy |= REQ_FSEQ_DATA; + + if (fflags & REQ_FLUSH) { + if (rq->cmd_flags & REQ_FLUSH) + policy |= REQ_FSEQ_PREFLUSH; + if (!(fflags & REQ_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->cmd_flags &= ~REQ_FLUSH_SEQ; + rq->end_io = rq->flush.saved_end_io; +} + +static bool blk_flush_queue_rq(struct request *rq, bool add_front) +{ + if (rq->q->mq_ops) { + struct request_queue *q = rq->q; + + blk_mq_add_to_requeue_list(rq, add_front); + blk_mq_kick_requeue_list(q); + return false; + } else { + if (add_front) + list_add(&rq->queuelist, &rq->q->queue_head); + else + list_add_tail(&rq->queuelist, &rq->q->queue_head); + return true; + } +} + +/** + * blk_flush_complete_seq - complete flush sequence + * @rq: FLUSH/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(q->queue_lock or fq->mq_flush_lock) + * + * RETURNS: + * %true if requests were added to the dispatch queue, %false otherwise. + */ +static bool blk_flush_complete_seq(struct request *rq, + struct blk_flush_queue *fq, + unsigned int seq, int error) +{ + struct request_queue *q = rq->q; + struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx]; + bool queued = false, kicked; + + BUG_ON(rq->flush.seq & seq); + rq->flush.seq |= seq; + + 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); + queued = blk_flush_queue_rq(rq, true); + break; + + case REQ_FSEQ_DONE: + /* + * @rq was previously adjusted by blk_flush_issue() for + * flush sequencing and may already have gone through the + * flush data request completion path. Restore @rq for + * normal completion and end it. + */ + BUG_ON(!list_empty(&rq->queuelist)); + list_del_init(&rq->flush.list); + blk_flush_restore_request(rq); + if (q->mq_ops) + blk_mq_end_request(rq, error); + else + __blk_end_request_all(rq, error); + break; + + default: + BUG(); + } + + kicked = blk_kick_flush(q, fq); + return kicked | queued; +} + +static void flush_end_io(struct request *flush_rq, int error) +{ + struct request_queue *q = flush_rq->q; + struct list_head *running; + bool queued = false; + struct request *rq, *n; + unsigned long flags = 0; + struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx); + + if (q->mq_ops) { + spin_lock_irqsave(&fq->mq_flush_lock, flags); + flush_rq->tag = -1; + } + + 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; + + if (!q->mq_ops) + elv_completed_request(q, flush_rq); + + /* 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); + queued |= blk_flush_complete_seq(rq, fq, seq, error); + } + + /* + * Kick the queue to avoid stall for two cases: + * 1. Moving a request silently to empty queue_head may stall the + * queue. + * 2. When flush request is running in non-queueable queue, the + * queue is hold. Restart the queue after flush request is finished + * to avoid stall. + * This function is called from request completion path and calling + * directly into request_fn may confuse the driver. Always use + * kblockd. + */ + if (queued || fq->flush_queue_delayed) { + WARN_ON(q->mq_ops); + blk_run_queue_async(q); + } + fq->flush_queue_delayed = 0; + if (q->mq_ops) + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); +} + +/** + * blk_kick_flush - consider issuing flush request + * @q: request_queue being kicked + * @fq: flush queue + * + * 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(q->queue_lock or fq->mq_flush_lock) + * + * RETURNS: + * %true if flush was issued, %false otherwise. + */ +static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq) +{ + 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 false; + + /* C2 and C3 */ + if (!list_empty(&fq->flush_data_in_flight) && + time_before(jiffies, + fq->flush_pending_since + FLUSH_PENDING_TIMEOUT)) + return false; + + /* + * 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); + + /* + * Borrow tag from the first request since they can't + * be in flight at the same time. + */ + if (q->mq_ops) { + flush_rq->mq_ctx = first_rq->mq_ctx; + flush_rq->tag = first_rq->tag; + } + + flush_rq->cmd_type = REQ_TYPE_FS; + flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ; + flush_rq->rq_disk = first_rq->rq_disk; + flush_rq->end_io = flush_end_io; + + return blk_flush_queue_rq(flush_rq, false); +} + +static void flush_data_end_io(struct request *rq, int error) +{ + struct request_queue *q = rq->q; + struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL); + + /* + * After populating an empty queue, kick it to avoid stall. Read + * the comment in flush_end_io(). + */ + if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error)) + blk_run_queue_async(q); +} + +static void mq_flush_data_end_io(struct request *rq, int error) +{ + struct request_queue *q = rq->q; + struct blk_mq_hw_ctx *hctx; + struct blk_mq_ctx *ctx = rq->mq_ctx; + unsigned long flags; + struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx); + + hctx = q->mq_ops->map_queue(q, ctx->cpu); + + /* + * 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); + if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error)) + blk_mq_run_hw_queue(hctx, true); + spin_unlock_irqrestore(&fq->mq_flush_lock, flags); +} + +/** + * blk_insert_flush - insert a new FLUSH/FUA request + * @rq: request to insert + * + * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions. + * or __blk_mq_run_hw_queue() to dispatch request. + * @rq is being submitted. Analyze what needs to be done and put it on the + * right queue. + * + * CONTEXT: + * spin_lock_irq(q->queue_lock) in !mq case + */ +void blk_insert_flush(struct request *rq) +{ + struct request_queue *q = rq->q; + unsigned int fflags = q->flush_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); + + /* + * @policy now records what operations need to be done. Adjust + * REQ_FLUSH and FUA for the driver. + */ + rq->cmd_flags &= ~REQ_FLUSH; + if (!(fflags & REQ_FUA)) + rq->cmd_flags &= ~REQ_FUA; + + /* + * 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. + */ + if (!policy) { + if (q->mq_ops) + blk_mq_end_request(rq, 0); + else + __blk_end_bidi_request(rq, 0, 0, 0); + return; + } + + BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */ + + /* + * If there's data but flush is not necessary, the request can be + * processed directly without going through flush machinery. Queue + * for normal execution. + */ + if ((policy & REQ_FSEQ_DATA) && + !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) { + if (q->mq_ops) { + blk_mq_insert_request(rq, false, false, true); + } else + list_add_tail(&rq->queuelist, &q->queue_head); + return; + } + + /* + * @rq should go through flush machinery. Mark it part of flush + * sequence and submit for further processing. + */ + memset(&rq->flush, 0, sizeof(rq->flush)); + INIT_LIST_HEAD(&rq->flush.list); + rq->cmd_flags |= REQ_FLUSH_SEQ; + rq->flush.saved_end_io = rq->end_io; /* Usually NULL */ + if (q->mq_ops) { + rq->end_io = mq_flush_data_end_io; + + 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; + } + rq->end_io = flush_data_end_io; + + blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0); +} + +/** + * blkdev_issue_flush - queue a flush + * @bdev: blockdev to issue flush for + * @gfp_mask: memory allocation flags (for bio_alloc) + * @error_sector: error sector + * + * Description: + * Issue a flush for the block device in question. Caller can supply + * room for storing the error offset in case of a flush error, if they + * wish to. If WAIT flag is not passed then caller may check only what + * request was pushed in some internal queue for later handling. + */ +int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, + sector_t *error_sector) +{ + struct request_queue *q; + struct bio *bio; + int ret = 0; + + if (bdev->bd_disk == NULL) + return -ENXIO; + + q = bdev_get_queue(bdev); + if (!q) + return -ENXIO; + + /* + * some block devices may not have their queue correctly set up here + * (e.g. loop device without a backing file) and so issuing a flush + * here will panic. Ensure there is a request function before issuing + * the flush. + */ + if (!q->make_request_fn) + return -ENXIO; + + bio = bio_alloc(gfp_mask, 0); + bio->bi_bdev = bdev; + + ret = submit_bio_wait(WRITE_FLUSH, bio); + + /* + * The driver must store the error location in ->bi_sector, if + * it supports it. For non-stacked drivers, this should be + * copied from blk_rq_pos(rq). + */ + if (error_sector) + *error_sector = bio->bi_iter.bi_sector; + + bio_put(bio); + return ret; +} +EXPORT_SYMBOL(blkdev_issue_flush); + +struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q, + int node, int cmd_size) +{ + struct blk_flush_queue *fq; + int rq_sz = sizeof(struct request); + + fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node); + if (!fq) + goto fail; + + if (q->mq_ops) { + 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, GFP_KERNEL, 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); +} |