/* * 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 (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; } /** * 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); } /* * 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 || q->flush_queue_delayed) blk_run_queue_async(q); q->flush_queue_delayed = 0; } /** * 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; list_add_tail(&q->flush_rq.queuelist, &q->queue_head); 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. Read * the comment in flush_end_io(). */ if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error)) blk_run_queue_async(q); } /** * 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. * @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); /* * @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) { __blk_end_bidi_request(rq, 0, 0, 0); return; } BUG_ON(!rq->bio || rq->bio != rq->biotail); /* * 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_tail(&rq->queuelist, &q->queue_head); blk_run_queue_async(q); 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 */ 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);