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2 * Functions to sequence PREFLUSH 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_{PREFLUSH|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_PREFLUSH makes sense, which
14 * indicates a simple flush request. If there is data, REQ_PREFLUSH 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, PREFLUSH and FUA don't make any
20 * difference. The requests are either completed immediately if there's no data
21 * or executed as normal requests otherwise.
23 * If the device has writeback cache and supports FUA, REQ_PREFLUSH 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_PREFLUSH
27 * is 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 * REQ_OP_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 PREFLUSH/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 PREFLUSH) requests.
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
55 * Note that a sequenced PREFLUSH/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 RQF_FLUSH_SEQ in
62 * The above peculiarity requires that each PREFLUSH/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>
76 #include "blk-mq-tag.h"
77 #include "blk-mq-sched.h"
79 /* PREFLUSH/FUA sequences */
81 REQ_FSEQ_PREFLUSH
= (1 << 0), /* pre-flushing in progress */
82 REQ_FSEQ_DATA
= (1 << 1), /* data write in progress */
83 REQ_FSEQ_POSTFLUSH
= (1 << 2), /* post-flushing in progress */
84 REQ_FSEQ_DONE
= (1 << 3),
86 REQ_FSEQ_ACTIONS
= REQ_FSEQ_PREFLUSH
| REQ_FSEQ_DATA
|
90 * If flush has been pending longer than the following timeout,
91 * it's issued even if flush_data requests are still in flight.
93 FLUSH_PENDING_TIMEOUT
= 5 * HZ
,
96 static bool blk_kick_flush(struct request_queue
*q
,
97 struct blk_flush_queue
*fq
, unsigned int flags
);
99 static unsigned int blk_flush_policy(unsigned long fflags
, struct request
*rq
)
101 unsigned int policy
= 0;
103 if (blk_rq_sectors(rq
))
104 policy
|= REQ_FSEQ_DATA
;
106 if (fflags
& (1UL << QUEUE_FLAG_WC
)) {
107 if (rq
->cmd_flags
& REQ_PREFLUSH
)
108 policy
|= REQ_FSEQ_PREFLUSH
;
109 if (!(fflags
& (1UL << QUEUE_FLAG_FUA
)) &&
110 (rq
->cmd_flags
& REQ_FUA
))
111 policy
|= REQ_FSEQ_POSTFLUSH
;
116 static unsigned int blk_flush_cur_seq(struct request
*rq
)
118 return 1 << ffz(rq
->flush
.seq
);
121 static void blk_flush_restore_request(struct request
*rq
)
124 * After flush data completion, @rq->bio is %NULL but we need to
125 * complete the bio again. @rq->biotail is guaranteed to equal the
126 * original @rq->bio. Restore it.
128 rq
->bio
= rq
->biotail
;
130 /* make @rq a normal request */
131 rq
->rq_flags
&= ~RQF_FLUSH_SEQ
;
132 rq
->end_io
= rq
->flush
.saved_end_io
;
135 static bool blk_flush_queue_rq(struct request
*rq
, bool add_front
)
138 blk_mq_add_to_requeue_list(rq
, add_front
, true);
142 list_add(&rq
->queuelist
, &rq
->q
->queue_head
);
144 list_add_tail(&rq
->queuelist
, &rq
->q
->queue_head
);
150 * blk_flush_complete_seq - complete flush sequence
151 * @rq: PREFLUSH/FUA request being sequenced
153 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
154 * @error: whether an error occurred
156 * @rq just completed @seq part of its flush sequence, record the
157 * completion and trigger the next step.
160 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
163 * %true if requests were added to the dispatch queue, %false otherwise.
165 static bool blk_flush_complete_seq(struct request
*rq
,
166 struct blk_flush_queue
*fq
,
167 unsigned int seq
, blk_status_t error
)
169 struct request_queue
*q
= rq
->q
;
170 struct list_head
*pending
= &fq
->flush_queue
[fq
->flush_pending_idx
];
171 bool queued
= false, kicked
;
172 unsigned int cmd_flags
;
174 BUG_ON(rq
->flush
.seq
& seq
);
175 rq
->flush
.seq
|= seq
;
176 cmd_flags
= rq
->cmd_flags
;
179 seq
= blk_flush_cur_seq(rq
);
184 case REQ_FSEQ_PREFLUSH
:
185 case REQ_FSEQ_POSTFLUSH
:
186 /* queue for flush */
187 if (list_empty(pending
))
188 fq
->flush_pending_since
= jiffies
;
189 list_move_tail(&rq
->flush
.list
, pending
);
193 list_move_tail(&rq
->flush
.list
, &fq
->flush_data_in_flight
);
194 queued
= blk_flush_queue_rq(rq
, true);
199 * @rq was previously adjusted by blk_flush_issue() for
200 * flush sequencing and may already have gone through the
201 * flush data request completion path. Restore @rq for
202 * normal completion and end it.
204 BUG_ON(!list_empty(&rq
->queuelist
));
205 list_del_init(&rq
->flush
.list
);
206 blk_flush_restore_request(rq
);
208 blk_mq_end_request(rq
, error
);
210 __blk_end_request_all(rq
, error
);
217 kicked
= blk_kick_flush(q
, fq
, cmd_flags
);
218 return kicked
| queued
;
221 static void flush_end_io(struct request
*flush_rq
, blk_status_t error
)
223 struct request_queue
*q
= flush_rq
->q
;
224 struct list_head
*running
;
226 struct request
*rq
, *n
;
227 unsigned long flags
= 0;
228 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, flush_rq
->mq_ctx
);
231 struct blk_mq_hw_ctx
*hctx
;
233 /* release the tag's ownership to the req cloned from */
234 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
235 hctx
= blk_mq_map_queue(q
, flush_rq
->mq_ctx
->cpu
);
237 blk_mq_tag_set_rq(hctx
, flush_rq
->tag
, fq
->orig_rq
);
240 blk_mq_put_driver_tag_hctx(hctx
, flush_rq
);
241 flush_rq
->internal_tag
= -1;
245 running
= &fq
->flush_queue
[fq
->flush_running_idx
];
246 BUG_ON(fq
->flush_pending_idx
== fq
->flush_running_idx
);
248 /* account completion of the flush request */
249 fq
->flush_running_idx
^= 1;
252 elv_completed_request(q
, flush_rq
);
254 /* and push the waiting requests to the next stage */
255 list_for_each_entry_safe(rq
, n
, running
, flush
.list
) {
256 unsigned int seq
= blk_flush_cur_seq(rq
);
258 BUG_ON(seq
!= REQ_FSEQ_PREFLUSH
&& seq
!= REQ_FSEQ_POSTFLUSH
);
259 queued
|= blk_flush_complete_seq(rq
, fq
, seq
, error
);
263 * Kick the queue to avoid stall for two cases:
264 * 1. Moving a request silently to empty queue_head may stall the
266 * 2. When flush request is running in non-queueable queue, the
267 * queue is hold. Restart the queue after flush request is finished
269 * This function is called from request completion path and calling
270 * directly into request_fn may confuse the driver. Always use
273 if (queued
|| fq
->flush_queue_delayed
) {
275 blk_run_queue_async(q
);
277 fq
->flush_queue_delayed
= 0;
279 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
283 * blk_kick_flush - consider issuing flush request
284 * @q: request_queue being kicked
286 * @flags: cmd_flags of the original request
288 * Flush related states of @q have changed, consider issuing flush request.
289 * Please read the comment at the top of this file for more info.
292 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
295 * %true if flush was issued, %false otherwise.
297 static bool blk_kick_flush(struct request_queue
*q
, struct blk_flush_queue
*fq
,
300 struct list_head
*pending
= &fq
->flush_queue
[fq
->flush_pending_idx
];
301 struct request
*first_rq
=
302 list_first_entry(pending
, struct request
, flush
.list
);
303 struct request
*flush_rq
= fq
->flush_rq
;
305 /* C1 described at the top of this file */
306 if (fq
->flush_pending_idx
!= fq
->flush_running_idx
|| list_empty(pending
))
311 * For blk-mq + scheduling, we can risk having all driver tags
312 * assigned to empty flushes, and we deadlock if we are expecting
313 * other requests to make progress. Don't defer for that case.
315 if (!list_empty(&fq
->flush_data_in_flight
) &&
316 !(q
->mq_ops
&& q
->elevator
) &&
318 fq
->flush_pending_since
+ FLUSH_PENDING_TIMEOUT
))
322 * Issue flush and toggle pending_idx. This makes pending_idx
323 * different from running_idx, which means flush is in flight.
325 fq
->flush_pending_idx
^= 1;
327 blk_rq_init(q
, flush_rq
);
330 * In case of none scheduler, borrow tag from the first request
331 * since they can't be in flight at the same time. And acquire
332 * the tag's ownership for flush req.
334 * In case of IO scheduler, flush rq need to borrow scheduler tag
335 * just for cheating put/get driver tag.
338 struct blk_mq_hw_ctx
*hctx
;
340 flush_rq
->mq_ctx
= first_rq
->mq_ctx
;
343 fq
->orig_rq
= first_rq
;
344 flush_rq
->tag
= first_rq
->tag
;
345 hctx
= blk_mq_map_queue(q
, first_rq
->mq_ctx
->cpu
);
346 blk_mq_tag_set_rq(hctx
, first_rq
->tag
, flush_rq
);
348 flush_rq
->internal_tag
= first_rq
->internal_tag
;
352 flush_rq
->cmd_flags
= REQ_OP_FLUSH
| REQ_PREFLUSH
;
353 flush_rq
->cmd_flags
|= (flags
& REQ_DRV
) | (flags
& REQ_FAILFAST_MASK
);
354 flush_rq
->rq_flags
|= RQF_FLUSH_SEQ
;
355 flush_rq
->rq_disk
= first_rq
->rq_disk
;
356 flush_rq
->end_io
= flush_end_io
;
358 return blk_flush_queue_rq(flush_rq
, false);
361 static void flush_data_end_io(struct request
*rq
, blk_status_t error
)
363 struct request_queue
*q
= rq
->q
;
364 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, NULL
);
366 lockdep_assert_held(q
->queue_lock
);
369 * Updating q->in_flight[] here for making this tag usable
370 * early. Because in blk_queue_start_tag(),
371 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
372 * reserve tags for sync I/O.
374 * More importantly this way can avoid the following I/O
377 * - suppose there are 40 fua requests comming to flush queue
378 * and queue depth is 31
379 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
380 * tag for async I/O any more
381 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
382 * and flush_data_end_io() is called
383 * - the other rqs still can't go ahead if not updating
384 * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
385 * are held in flush data queue and make no progress of
386 * handling post flush rq
387 * - only after the post flush rq is handled, all these rqs
391 elv_completed_request(q
, rq
);
393 /* for avoiding double accounting */
394 rq
->rq_flags
&= ~RQF_STARTED
;
397 * After populating an empty queue, kick it to avoid stall. Read
398 * the comment in flush_end_io().
400 if (blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_DATA
, error
))
401 blk_run_queue_async(q
);
404 static void mq_flush_data_end_io(struct request
*rq
, blk_status_t error
)
406 struct request_queue
*q
= rq
->q
;
407 struct blk_mq_hw_ctx
*hctx
;
408 struct blk_mq_ctx
*ctx
= rq
->mq_ctx
;
410 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, ctx
);
412 hctx
= blk_mq_map_queue(q
, ctx
->cpu
);
415 WARN_ON(rq
->tag
< 0);
416 blk_mq_put_driver_tag_hctx(hctx
, rq
);
420 * After populating an empty queue, kick it to avoid stall. Read
421 * the comment in flush_end_io().
423 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
424 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_DATA
, error
);
425 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
427 blk_mq_run_hw_queue(hctx
, true);
431 * blk_insert_flush - insert a new PREFLUSH/FUA request
432 * @rq: request to insert
434 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
435 * or __blk_mq_run_hw_queue() to dispatch request.
436 * @rq is being submitted. Analyze what needs to be done and put it on the
439 void blk_insert_flush(struct request
*rq
)
441 struct request_queue
*q
= rq
->q
;
442 unsigned long fflags
= q
->queue_flags
; /* may change, cache */
443 unsigned int policy
= blk_flush_policy(fflags
, rq
);
444 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, rq
->mq_ctx
);
447 lockdep_assert_held(q
->queue_lock
);
450 * @policy now records what operations need to be done. Adjust
451 * REQ_PREFLUSH and FUA for the driver.
453 rq
->cmd_flags
&= ~REQ_PREFLUSH
;
454 if (!(fflags
& (1UL << QUEUE_FLAG_FUA
)))
455 rq
->cmd_flags
&= ~REQ_FUA
;
458 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
459 * of those flags, we have to set REQ_SYNC to avoid skewing
460 * the request accounting.
462 rq
->cmd_flags
|= REQ_SYNC
;
465 * An empty flush handed down from a stacking driver may
466 * translate into nothing if the underlying device does not
467 * advertise a write-back cache. In this case, simply
468 * complete the request.
472 blk_mq_end_request(rq
, 0);
474 __blk_end_request(rq
, 0, 0);
478 BUG_ON(rq
->bio
!= rq
->biotail
); /*assumes zero or single bio rq */
481 * If there's data but flush is not necessary, the request can be
482 * processed directly without going through flush machinery. Queue
483 * for normal execution.
485 if ((policy
& REQ_FSEQ_DATA
) &&
486 !(policy
& (REQ_FSEQ_PREFLUSH
| REQ_FSEQ_POSTFLUSH
))) {
488 blk_mq_request_bypass_insert(rq
, false);
490 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
495 * @rq should go through flush machinery. Mark it part of flush
496 * sequence and submit for further processing.
498 memset(&rq
->flush
, 0, sizeof(rq
->flush
));
499 INIT_LIST_HEAD(&rq
->flush
.list
);
500 rq
->rq_flags
|= RQF_FLUSH_SEQ
;
501 rq
->flush
.saved_end_io
= rq
->end_io
; /* Usually NULL */
503 rq
->end_io
= mq_flush_data_end_io
;
505 spin_lock_irq(&fq
->mq_flush_lock
);
506 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
507 spin_unlock_irq(&fq
->mq_flush_lock
);
510 rq
->end_io
= flush_data_end_io
;
512 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
516 * blkdev_issue_flush - queue a flush
517 * @bdev: blockdev to issue flush for
518 * @gfp_mask: memory allocation flags (for bio_alloc)
519 * @error_sector: error sector
522 * Issue a flush for the block device in question. Caller can supply
523 * room for storing the error offset in case of a flush error, if they
526 int blkdev_issue_flush(struct block_device
*bdev
, gfp_t gfp_mask
,
527 sector_t
*error_sector
)
529 struct request_queue
*q
;
533 if (bdev
->bd_disk
== NULL
)
536 q
= bdev_get_queue(bdev
);
541 * some block devices may not have their queue correctly set up here
542 * (e.g. loop device without a backing file) and so issuing a flush
543 * here will panic. Ensure there is a request function before issuing
546 if (!q
->make_request_fn
)
549 bio
= bio_alloc(gfp_mask
, 0);
550 bio_set_dev(bio
, bdev
);
551 bio
->bi_opf
= REQ_OP_WRITE
| REQ_PREFLUSH
;
553 ret
= submit_bio_wait(bio
);
556 * The driver must store the error location in ->bi_sector, if
557 * it supports it. For non-stacked drivers, this should be
558 * copied from blk_rq_pos(rq).
561 *error_sector
= bio
->bi_iter
.bi_sector
;
566 EXPORT_SYMBOL(blkdev_issue_flush
);
568 struct blk_flush_queue
*blk_alloc_flush_queue(struct request_queue
*q
,
569 int node
, int cmd_size
, gfp_t flags
)
571 struct blk_flush_queue
*fq
;
572 int rq_sz
= sizeof(struct request
);
574 fq
= kzalloc_node(sizeof(*fq
), flags
, node
);
579 spin_lock_init(&fq
->mq_flush_lock
);
581 rq_sz
= round_up(rq_sz
+ cmd_size
, cache_line_size());
582 fq
->flush_rq
= kzalloc_node(rq_sz
, flags
, node
);
586 INIT_LIST_HEAD(&fq
->flush_queue
[0]);
587 INIT_LIST_HEAD(&fq
->flush_queue
[1]);
588 INIT_LIST_HEAD(&fq
->flush_data_in_flight
);
598 void blk_free_flush_queue(struct blk_flush_queue
*fq
)
600 /* bio based request queue hasn't flush queue */