2 * Functions to sequence FLUSH and FUA writes.
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
7 * This file is released under the GPLv2.
9 * REQ_{FLUSH|FUA} requests are decomposed to sequences consisted of three
10 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
11 * properties and hardware capability.
13 * If a request doesn't have data, only REQ_FLUSH makes sense, which
14 * indicates a simple flush request. If there is data, REQ_FLUSH indicates
15 * that the device cache should be flushed before the data is executed, and
16 * REQ_FUA means that the data must be on non-volatile media on request
19 * If the device doesn't have writeback cache, FLUSH and FUA don't make any
20 * difference. The requests are either completed immediately if there's no
21 * data or executed as normal requests otherwise.
23 * If the device has writeback cache and supports FUA, REQ_FLUSH is
24 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
26 * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
27 * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
29 * The actual execution of flush is double buffered. Whenever a request
30 * needs to execute PRE or POSTFLUSH, it queues at
31 * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
32 * flush is issued and the pending_idx is toggled. When the flush
33 * completes, all the requests which were pending are proceeded to the next
34 * step. This allows arbitrary merging of different types of FLUSH/FUA
37 * Currently, the following conditions are used to determine when to issue
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
47 * C3. The second condition is ignored if there is a request which has
48 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
49 * starvation in the unlikely case where there are continuous stream of
50 * FUA (without FLUSH) requests.
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
55 * Note that a sequenced FLUSH/FUA request with DATA is completed twice.
56 * Once while executing DATA and again after the whole sequence is
57 * complete. The first completion updates the contained bio but doesn't
58 * finish it so that the bio submitter is notified only after the whole
59 * sequence is complete. This is implemented by testing REQ_FLUSH_SEQ in
62 * The above peculiarity requires that each FLUSH/FUA request has only one
63 * bio attached to it, which is guaranteed as they aren't allowed to be
64 * merged in the usual way.
67 #include <linux/kernel.h>
68 #include <linux/module.h>
69 #include <linux/bio.h>
70 #include <linux/blkdev.h>
71 #include <linux/gfp.h>
72 #include <linux/blk-mq.h>
77 /* FLUSH/FUA sequences */
79 REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
80 REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
81 REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
82 REQ_FSEQ_DONE = (1 << 3),
84 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
88 * If flush has been pending longer than the following timeout,
89 * it's issued even if flush_data requests are still in flight.
91 FLUSH_PENDING_TIMEOUT = 5 * HZ,
94 static bool blk_kick_flush(struct request_queue *q);
96 static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
98 unsigned int policy = 0;
100 if (blk_rq_sectors(rq))
101 policy |= REQ_FSEQ_DATA;
103 if (fflags & REQ_FLUSH) {
104 if (rq->cmd_flags & REQ_FLUSH)
105 policy |= REQ_FSEQ_PREFLUSH;
106 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
107 policy |= REQ_FSEQ_POSTFLUSH;
112 static unsigned int blk_flush_cur_seq(struct request *rq)
114 return 1 << ffz(rq->flush.seq);
117 static void blk_flush_restore_request(struct request *rq)
120 * After flush data completion, @rq->bio is %NULL but we need to
121 * complete the bio again. @rq->biotail is guaranteed to equal the
122 * original @rq->bio. Restore it.
124 rq->bio = rq->biotail;
126 /* make @rq a normal request */
127 rq->cmd_flags &= ~REQ_FLUSH_SEQ;
128 rq->end_io = rq->flush.saved_end_io;
131 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
134 struct request_queue *q = rq->q;
136 blk_mq_add_to_requeue_list(rq, add_front);
137 blk_mq_kick_requeue_list(q);
141 list_add(&rq->queuelist, &rq->q->queue_head);
143 list_add_tail(&rq->queuelist, &rq->q->queue_head);
149 * blk_flush_complete_seq - complete flush sequence
150 * @rq: FLUSH/FUA request being sequenced
151 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
152 * @error: whether an error occurred
154 * @rq just completed @seq part of its flush sequence, record the
155 * completion and trigger the next step.
158 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
161 * %true if requests were added to the dispatch queue, %false otherwise.
163 static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
166 struct request_queue *q = rq->q;
167 struct blk_flush_queue *fq = blk_get_flush_queue(q);
168 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
169 bool queued = false, kicked;
171 BUG_ON(rq->flush.seq & seq);
172 rq->flush.seq |= seq;
175 seq = blk_flush_cur_seq(rq);
180 case REQ_FSEQ_PREFLUSH:
181 case REQ_FSEQ_POSTFLUSH:
182 /* queue for flush */
183 if (list_empty(pending))
184 fq->flush_pending_since = jiffies;
185 list_move_tail(&rq->flush.list, pending);
189 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
190 queued = blk_flush_queue_rq(rq, true);
195 * @rq was previously adjusted by blk_flush_issue() for
196 * flush sequencing and may already have gone through the
197 * flush data request completion path. Restore @rq for
198 * normal completion and end it.
200 BUG_ON(!list_empty(&rq->queuelist));
201 list_del_init(&rq->flush.list);
202 blk_flush_restore_request(rq);
204 blk_mq_end_request(rq, error);
206 __blk_end_request_all(rq, error);
213 kicked = blk_kick_flush(q);
214 return kicked | queued;
217 static void flush_end_io(struct request *flush_rq, int error)
219 struct request_queue *q = flush_rq->q;
220 struct list_head *running;
222 struct request *rq, *n;
223 unsigned long flags = 0;
224 struct blk_flush_queue *fq = blk_get_flush_queue(q);
227 spin_lock_irqsave(&fq->mq_flush_lock, flags);
231 running = &fq->flush_queue[fq->flush_running_idx];
232 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
234 /* account completion of the flush request */
235 fq->flush_running_idx ^= 1;
238 elv_completed_request(q, flush_rq);
240 /* and push the waiting requests to the next stage */
241 list_for_each_entry_safe(rq, n, running, flush.list) {
242 unsigned int seq = blk_flush_cur_seq(rq);
244 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
245 queued |= blk_flush_complete_seq(rq, seq, error);
249 * Kick the queue to avoid stall for two cases:
250 * 1. Moving a request silently to empty queue_head may stall the
252 * 2. When flush request is running in non-queueable queue, the
253 * queue is hold. Restart the queue after flush request is finished
255 * This function is called from request completion path and calling
256 * directly into request_fn may confuse the driver. Always use
259 if (queued || fq->flush_queue_delayed) {
261 blk_run_queue_async(q);
263 fq->flush_queue_delayed = 0;
265 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
269 * blk_kick_flush - consider issuing flush request
270 * @q: request_queue being kicked
272 * Flush related states of @q have changed, consider issuing flush request.
273 * Please read the comment at the top of this file for more info.
276 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
279 * %true if flush was issued, %false otherwise.
281 static bool blk_kick_flush(struct request_queue *q)
283 struct blk_flush_queue *fq = blk_get_flush_queue(q);
284 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
285 struct request *first_rq =
286 list_first_entry(pending, struct request, flush.list);
287 struct request *flush_rq = fq->flush_rq;
289 /* C1 described at the top of this file */
290 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
294 if (!list_empty(&fq->flush_data_in_flight) &&
296 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
300 * Issue flush and toggle pending_idx. This makes pending_idx
301 * different from running_idx, which means flush is in flight.
303 fq->flush_pending_idx ^= 1;
305 blk_rq_init(q, flush_rq);
307 blk_mq_clone_flush_request(flush_rq, first_rq);
309 flush_rq->cmd_type = REQ_TYPE_FS;
310 flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
311 flush_rq->rq_disk = first_rq->rq_disk;
312 flush_rq->end_io = flush_end_io;
314 return blk_flush_queue_rq(flush_rq, false);
317 static void flush_data_end_io(struct request *rq, int error)
319 struct request_queue *q = rq->q;
322 * After populating an empty queue, kick it to avoid stall. Read
323 * the comment in flush_end_io().
325 if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
326 blk_run_queue_async(q);
329 static void mq_flush_data_end_io(struct request *rq, int error)
331 struct request_queue *q = rq->q;
332 struct blk_mq_hw_ctx *hctx;
333 struct blk_mq_ctx *ctx;
335 struct blk_flush_queue *fq = blk_get_flush_queue(q);
338 hctx = q->mq_ops->map_queue(q, ctx->cpu);
341 * After populating an empty queue, kick it to avoid stall. Read
342 * the comment in flush_end_io().
344 spin_lock_irqsave(&fq->mq_flush_lock, flags);
345 if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
346 blk_mq_run_hw_queue(hctx, true);
347 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
351 * blk_insert_flush - insert a new FLUSH/FUA request
352 * @rq: request to insert
354 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
355 * or __blk_mq_run_hw_queue() to dispatch request.
356 * @rq is being submitted. Analyze what needs to be done and put it on the
360 * spin_lock_irq(q->queue_lock) in !mq case
362 void blk_insert_flush(struct request *rq)
364 struct request_queue *q = rq->q;
365 unsigned int fflags = q->flush_flags; /* may change, cache */
366 unsigned int policy = blk_flush_policy(fflags, rq);
369 * @policy now records what operations need to be done. Adjust
370 * REQ_FLUSH and FUA for the driver.
372 rq->cmd_flags &= ~REQ_FLUSH;
373 if (!(fflags & REQ_FUA))
374 rq->cmd_flags &= ~REQ_FUA;
377 * An empty flush handed down from a stacking driver may
378 * translate into nothing if the underlying device does not
379 * advertise a write-back cache. In this case, simply
380 * complete the request.
384 blk_mq_end_request(rq, 0);
386 __blk_end_bidi_request(rq, 0, 0, 0);
390 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
393 * If there's data but flush is not necessary, the request can be
394 * processed directly without going through flush machinery. Queue
395 * for normal execution.
397 if ((policy & REQ_FSEQ_DATA) &&
398 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
400 blk_mq_insert_request(rq, false, false, true);
402 list_add_tail(&rq->queuelist, &q->queue_head);
407 * @rq should go through flush machinery. Mark it part of flush
408 * sequence and submit for further processing.
410 memset(&rq->flush, 0, sizeof(rq->flush));
411 INIT_LIST_HEAD(&rq->flush.list);
412 rq->cmd_flags |= REQ_FLUSH_SEQ;
413 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
415 struct blk_flush_queue *fq = blk_get_flush_queue(q);
417 rq->end_io = mq_flush_data_end_io;
419 spin_lock_irq(&fq->mq_flush_lock);
420 blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
421 spin_unlock_irq(&fq->mq_flush_lock);
424 rq->end_io = flush_data_end_io;
426 blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
430 * blkdev_issue_flush - queue a flush
431 * @bdev: blockdev to issue flush for
432 * @gfp_mask: memory allocation flags (for bio_alloc)
433 * @error_sector: error sector
436 * Issue a flush for the block device in question. Caller can supply
437 * room for storing the error offset in case of a flush error, if they
438 * wish to. If WAIT flag is not passed then caller may check only what
439 * request was pushed in some internal queue for later handling.
441 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
442 sector_t *error_sector)
444 struct request_queue *q;
448 if (bdev->bd_disk == NULL)
451 q = bdev_get_queue(bdev);
456 * some block devices may not have their queue correctly set up here
457 * (e.g. loop device without a backing file) and so issuing a flush
458 * here will panic. Ensure there is a request function before issuing
461 if (!q->make_request_fn)
464 bio = bio_alloc(gfp_mask, 0);
467 ret = submit_bio_wait(WRITE_FLUSH, bio);
470 * The driver must store the error location in ->bi_sector, if
471 * it supports it. For non-stacked drivers, this should be
472 * copied from blk_rq_pos(rq).
475 *error_sector = bio->bi_iter.bi_sector;
480 EXPORT_SYMBOL(blkdev_issue_flush);
482 static struct blk_flush_queue *blk_alloc_flush_queue(
483 struct request_queue *q)
485 struct blk_flush_queue *fq;
486 int rq_sz = sizeof(struct request);
488 fq = kzalloc(sizeof(*fq), GFP_KERNEL);
493 spin_lock_init(&fq->mq_flush_lock);
494 rq_sz = round_up(rq_sz + q->tag_set->cmd_size,
498 fq->flush_rq = kzalloc(rq_sz, GFP_KERNEL);
502 INIT_LIST_HEAD(&fq->flush_queue[0]);
503 INIT_LIST_HEAD(&fq->flush_queue[1]);
504 INIT_LIST_HEAD(&fq->flush_data_in_flight);
514 static void blk_free_flush_queue(struct blk_flush_queue *fq)
516 /* bio based request queue hasn't flush queue */
524 int blk_init_flush(struct request_queue *q)
526 q->fq = blk_alloc_flush_queue(q);
533 void blk_exit_flush(struct request_queue *q)
535 blk_free_flush_queue(q->fq);