| /* |
| * 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 |
| * q->flush_queue[q->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 "blk.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); |
| |
| static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq) |
| { |
| unsigned int policy = 0; |
| |
| if (fflags & REQ_FLUSH) { |
| if (rq->cmd_flags & REQ_FLUSH) |
| policy |= REQ_FSEQ_PREFLUSH; |
| if (blk_rq_sectors(rq)) |
| policy |= REQ_FSEQ_DATA; |
| 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 = NULL; |
| } |
| |
| /** |
| * blk_flush_complete_seq - complete flush sequence |
| * @rq: FLUSH/FUA request being sequenced |
| * @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) |
| * |
| * RETURNS: |
| * %true if requests were added to the dispatch queue, %false otherwise. |
| */ |
| static bool blk_flush_complete_seq(struct request *rq, unsigned int seq, |
| int error) |
| { |
| struct request_queue *q = rq->q; |
| struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; |
| bool queued = false; |
| |
| 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)) |
| q->flush_pending_since = jiffies; |
| list_move_tail(&rq->flush.list, pending); |
| break; |
| |
| case REQ_FSEQ_DATA: |
| list_move_tail(&rq->flush.list, &q->flush_data_in_flight); |
| list_add(&rq->queuelist, &q->queue_head); |
| queued = 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); |
| __blk_end_request_all(rq, error); |
| break; |
| |
| default: |
| BUG(); |
| } |
| |
| return blk_kick_flush(q) | queued; |
| } |
| |
| static void flush_end_io(struct request *flush_rq, int error) |
| { |
| struct request_queue *q = flush_rq->q; |
| struct list_head *running = &q->flush_queue[q->flush_running_idx]; |
| bool queued = false; |
| struct request *rq, *n; |
| |
| BUG_ON(q->flush_pending_idx == q->flush_running_idx); |
| |
| /* account completion of the flush request */ |
| q->flush_running_idx ^= 1; |
| 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, seq, error); |
| } |
| |
| /* after populating an empty queue, kick it to avoid stall */ |
| if (queued) |
| __blk_run_queue(q); |
| } |
| |
| /** |
| * blk_kick_flush - consider issuing flush request |
| * @q: request_queue being kicked |
| * |
| * 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) |
| * |
| * RETURNS: |
| * %true if flush was issued, %false otherwise. |
| */ |
| static bool blk_kick_flush(struct request_queue *q) |
| { |
| struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; |
| struct request *first_rq = |
| list_first_entry(pending, struct request, flush.list); |
| |
| /* C1 described at the top of this file */ |
| if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending)) |
| return false; |
| |
| /* C2 and C3 */ |
| if (!list_empty(&q->flush_data_in_flight) && |
| time_before(jiffies, |
| q->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. |
| */ |
| blk_rq_init(q, &q->flush_rq); |
| q->flush_rq.cmd_type = REQ_TYPE_FS; |
| q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ; |
| q->flush_rq.rq_disk = first_rq->rq_disk; |
| q->flush_rq.end_io = flush_end_io; |
| |
| q->flush_pending_idx ^= 1; |
| elv_insert(q, &q->flush_rq, ELEVATOR_INSERT_FRONT); |
| return true; |
| } |
| |
| static void flush_data_end_io(struct request *rq, int error) |
| { |
| struct request_queue *q = rq->q; |
| |
| /* after populating an empty queue, kick it to avoid stall */ |
| if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error)) |
| __blk_run_queue(q); |
| } |
| |
| /** |
| * blk_insert_flush - insert a new FLUSH/FUA request |
| * @rq: request to insert |
| * |
| * To be called from elv_insert() for %ELEVATOR_INSERT_FLUSH insertions. |
| * @rq is being submitted. Analyze what needs to be done and put it on the |
| * right queue. |
| * |
| * CONTEXT: |
| * spin_lock_irq(q->queue_lock) |
| */ |
| 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); |
| |
| BUG_ON(rq->end_io); |
| BUG_ON(!rq->bio || rq->bio != rq->biotail); |
| |
| /* |
| * @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; |
| |
| /* |
| * 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))) { |
| list_add(&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->end_io = flush_data_end_io; |
| |
| blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0); |
| } |
| |
| /** |
| * blk_abort_flushes - @q is being aborted, abort flush requests |
| * @q: request_queue being aborted |
| * |
| * To be called from elv_abort_queue(). @q is being aborted. Prepare all |
| * FLUSH/FUA requests for abortion. |
| * |
| * CONTEXT: |
| * spin_lock_irq(q->queue_lock) |
| */ |
| void blk_abort_flushes(struct request_queue *q) |
| { |
| struct request *rq, *n; |
| int i; |
| |
| /* |
| * Requests in flight for data are already owned by the dispatch |
| * queue or the device driver. Just restore for normal completion. |
| */ |
| list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) { |
| list_del_init(&rq->flush.list); |
| blk_flush_restore_request(rq); |
| } |
| |
| /* |
| * We need to give away requests on flush queues. Restore for |
| * normal completion and put them on the dispatch queue. |
| */ |
| for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) { |
| list_for_each_entry_safe(rq, n, &q->flush_queue[i], |
| flush.list) { |
| list_del_init(&rq->flush.list); |
| blk_flush_restore_request(rq); |
| list_add_tail(&rq->queuelist, &q->queue_head); |
| } |
| } |
| } |
| |
| static void bio_end_flush(struct bio *bio, int err) |
| { |
| if (err) |
| clear_bit(BIO_UPTODATE, &bio->bi_flags); |
| if (bio->bi_private) |
| complete(bio->bi_private); |
| bio_put(bio); |
| } |
| |
| /** |
| * 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) |
| { |
| DECLARE_COMPLETION_ONSTACK(wait); |
| 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_end_io = bio_end_flush; |
| bio->bi_bdev = bdev; |
| bio->bi_private = &wait; |
| |
| bio_get(bio); |
| submit_bio(WRITE_FLUSH, bio); |
| wait_for_completion(&wait); |
| |
| /* |
| * 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_sector; |
| |
| if (!bio_flagged(bio, BIO_UPTODATE)) |
| ret = -EIO; |
| |
| bio_put(bio); |
| return ret; |
| } |
| EXPORT_SYMBOL(blkdev_issue_flush); |