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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_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, 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_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 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 RQF_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>
76 #include "blk-mq-tag.h"
77 #include "blk-mq-sched.h"
79 /* FLUSH/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
);
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: FLUSH/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
, int 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
;
173 BUG_ON(rq
->flush
.seq
& seq
);
174 rq
->flush
.seq
|= seq
;
177 seq
= blk_flush_cur_seq(rq
);
182 case REQ_FSEQ_PREFLUSH
:
183 case REQ_FSEQ_POSTFLUSH
:
184 /* queue for flush */
185 if (list_empty(pending
))
186 fq
->flush_pending_since
= jiffies
;
187 list_move_tail(&rq
->flush
.list
, pending
);
191 list_move_tail(&rq
->flush
.list
, &fq
->flush_data_in_flight
);
192 queued
= blk_flush_queue_rq(rq
, true);
197 * @rq was previously adjusted by blk_flush_issue() for
198 * flush sequencing and may already have gone through the
199 * flush data request completion path. Restore @rq for
200 * normal completion and end it.
202 BUG_ON(!list_empty(&rq
->queuelist
));
203 list_del_init(&rq
->flush
.list
);
204 blk_flush_restore_request(rq
);
206 blk_mq_end_request(rq
, error
);
208 __blk_end_request_all(rq
, error
);
215 kicked
= blk_kick_flush(q
, fq
);
216 return kicked
| queued
;
219 static void flush_end_io(struct request
*flush_rq
, int error
)
221 struct request_queue
*q
= flush_rq
->q
;
222 struct list_head
*running
;
224 struct request
*rq
, *n
;
225 unsigned long flags
= 0;
226 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, flush_rq
->mq_ctx
);
229 struct blk_mq_hw_ctx
*hctx
;
231 /* release the tag's ownership to the req cloned from */
232 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
233 hctx
= blk_mq_map_queue(q
, flush_rq
->mq_ctx
->cpu
);
234 blk_mq_tag_set_rq(hctx
, flush_rq
->tag
, fq
->orig_rq
);
238 running
= &fq
->flush_queue
[fq
->flush_running_idx
];
239 BUG_ON(fq
->flush_pending_idx
== fq
->flush_running_idx
);
241 /* account completion of the flush request */
242 fq
->flush_running_idx
^= 1;
245 elv_completed_request(q
, flush_rq
);
247 /* and push the waiting requests to the next stage */
248 list_for_each_entry_safe(rq
, n
, running
, flush
.list
) {
249 unsigned int seq
= blk_flush_cur_seq(rq
);
251 BUG_ON(seq
!= REQ_FSEQ_PREFLUSH
&& seq
!= REQ_FSEQ_POSTFLUSH
);
252 queued
|= blk_flush_complete_seq(rq
, fq
, seq
, error
);
256 * Kick the queue to avoid stall for two cases:
257 * 1. Moving a request silently to empty queue_head may stall the
259 * 2. When flush request is running in non-queueable queue, the
260 * queue is hold. Restart the queue after flush request is finished
262 * This function is called from request completion path and calling
263 * directly into request_fn may confuse the driver. Always use
266 if (queued
|| fq
->flush_queue_delayed
) {
268 blk_run_queue_async(q
);
270 fq
->flush_queue_delayed
= 0;
272 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
276 * blk_kick_flush - consider issuing flush request
277 * @q: request_queue being kicked
280 * Flush related states of @q have changed, consider issuing flush request.
281 * Please read the comment at the top of this file for more info.
284 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
287 * %true if flush was issued, %false otherwise.
289 static bool blk_kick_flush(struct request_queue
*q
, struct blk_flush_queue
*fq
)
291 struct list_head
*pending
= &fq
->flush_queue
[fq
->flush_pending_idx
];
292 struct request
*first_rq
=
293 list_first_entry(pending
, struct request
, flush
.list
);
294 struct request
*flush_rq
= fq
->flush_rq
;
296 /* C1 described at the top of this file */
297 if (fq
->flush_pending_idx
!= fq
->flush_running_idx
|| list_empty(pending
))
302 * For blk-mq + scheduling, we can risk having all driver tags
303 * assigned to empty flushes, and we deadlock if we are expecting
304 * other requests to make progress. Don't defer for that case.
306 if (!list_empty(&fq
->flush_data_in_flight
) &&
307 !(q
->mq_ops
&& q
->elevator
) &&
309 fq
->flush_pending_since
+ FLUSH_PENDING_TIMEOUT
))
313 * Issue flush and toggle pending_idx. This makes pending_idx
314 * different from running_idx, which means flush is in flight.
316 fq
->flush_pending_idx
^= 1;
318 blk_rq_init(q
, flush_rq
);
321 * Borrow tag from the first request since they can't
322 * be in flight at the same time. And acquire the tag's
323 * ownership for flush req.
326 struct blk_mq_hw_ctx
*hctx
;
328 flush_rq
->mq_ctx
= first_rq
->mq_ctx
;
329 flush_rq
->tag
= first_rq
->tag
;
330 fq
->orig_rq
= first_rq
;
332 hctx
= blk_mq_map_queue(q
, first_rq
->mq_ctx
->cpu
);
333 blk_mq_tag_set_rq(hctx
, first_rq
->tag
, flush_rq
);
336 flush_rq
->cmd_flags
= REQ_OP_FLUSH
| REQ_PREFLUSH
;
337 flush_rq
->rq_flags
|= RQF_FLUSH_SEQ
;
338 flush_rq
->rq_disk
= first_rq
->rq_disk
;
339 flush_rq
->end_io
= flush_end_io
;
341 return blk_flush_queue_rq(flush_rq
, false);
344 static void flush_data_end_io(struct request
*rq
, int error
)
346 struct request_queue
*q
= rq
->q
;
347 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, NULL
);
350 * Updating q->in_flight[] here for making this tag usable
351 * early. Because in blk_queue_start_tag(),
352 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
353 * reserve tags for sync I/O.
355 * More importantly this way can avoid the following I/O
358 * - suppose there are 40 fua requests comming to flush queue
359 * and queue depth is 31
360 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
361 * tag for async I/O any more
362 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
363 * and flush_data_end_io() is called
364 * - the other rqs still can't go ahead if not updating
365 * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
366 * are held in flush data queue and make no progress of
367 * handling post flush rq
368 * - only after the post flush rq is handled, all these rqs
372 elv_completed_request(q
, rq
);
374 /* for avoiding double accounting */
375 rq
->rq_flags
&= ~RQF_STARTED
;
378 * After populating an empty queue, kick it to avoid stall. Read
379 * the comment in flush_end_io().
381 if (blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_DATA
, error
))
382 blk_run_queue_async(q
);
385 static void mq_flush_data_end_io(struct request
*rq
, int error
)
387 struct request_queue
*q
= rq
->q
;
388 struct blk_mq_hw_ctx
*hctx
;
389 struct blk_mq_ctx
*ctx
= rq
->mq_ctx
;
391 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, ctx
);
393 hctx
= blk_mq_map_queue(q
, ctx
->cpu
);
396 * After populating an empty queue, kick it to avoid stall. Read
397 * the comment in flush_end_io().
399 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
400 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_DATA
, error
);
401 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
403 blk_mq_run_hw_queue(hctx
, true);
407 * blk_insert_flush - insert a new FLUSH/FUA request
408 * @rq: request to insert
410 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
411 * or __blk_mq_run_hw_queue() to dispatch request.
412 * @rq is being submitted. Analyze what needs to be done and put it on the
416 * spin_lock_irq(q->queue_lock) in !mq case
418 void blk_insert_flush(struct request
*rq
)
420 struct request_queue
*q
= rq
->q
;
421 unsigned long fflags
= q
->queue_flags
; /* may change, cache */
422 unsigned int policy
= blk_flush_policy(fflags
, rq
);
423 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, rq
->mq_ctx
);
426 * @policy now records what operations need to be done. Adjust
427 * REQ_PREFLUSH and FUA for the driver.
429 rq
->cmd_flags
&= ~REQ_PREFLUSH
;
430 if (!(fflags
& (1UL << QUEUE_FLAG_FUA
)))
431 rq
->cmd_flags
&= ~REQ_FUA
;
434 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
435 * of those flags, we have to set REQ_SYNC to avoid skewing
436 * the request accounting.
438 rq
->cmd_flags
|= REQ_SYNC
;
441 * An empty flush handed down from a stacking driver may
442 * translate into nothing if the underlying device does not
443 * advertise a write-back cache. In this case, simply
444 * complete the request.
448 blk_mq_end_request(rq
, 0);
450 __blk_end_bidi_request(rq
, 0, 0, 0);
454 BUG_ON(rq
->bio
!= rq
->biotail
); /*assumes zero or single bio rq */
457 * If there's data but flush is not necessary, the request can be
458 * processed directly without going through flush machinery. Queue
459 * for normal execution.
461 if ((policy
& REQ_FSEQ_DATA
) &&
462 !(policy
& (REQ_FSEQ_PREFLUSH
| REQ_FSEQ_POSTFLUSH
))) {
464 blk_mq_sched_insert_request(rq
, false, true, false, false);
466 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
471 * @rq should go through flush machinery. Mark it part of flush
472 * sequence and submit for further processing.
474 memset(&rq
->flush
, 0, sizeof(rq
->flush
));
475 INIT_LIST_HEAD(&rq
->flush
.list
);
476 rq
->rq_flags
|= RQF_FLUSH_SEQ
;
477 rq
->flush
.saved_end_io
= rq
->end_io
; /* Usually NULL */
479 rq
->end_io
= mq_flush_data_end_io
;
481 spin_lock_irq(&fq
->mq_flush_lock
);
482 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
483 spin_unlock_irq(&fq
->mq_flush_lock
);
486 rq
->end_io
= flush_data_end_io
;
488 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
492 * blkdev_issue_flush - queue a flush
493 * @bdev: blockdev to issue flush for
494 * @gfp_mask: memory allocation flags (for bio_alloc)
495 * @error_sector: error sector
498 * Issue a flush for the block device in question. Caller can supply
499 * room for storing the error offset in case of a flush error, if they
500 * wish to. If WAIT flag is not passed then caller may check only what
501 * request was pushed in some internal queue for later handling.
503 int blkdev_issue_flush(struct block_device
*bdev
, gfp_t gfp_mask
,
504 sector_t
*error_sector
)
506 struct request_queue
*q
;
510 if (bdev
->bd_disk
== NULL
)
513 q
= bdev_get_queue(bdev
);
518 * some block devices may not have their queue correctly set up here
519 * (e.g. loop device without a backing file) and so issuing a flush
520 * here will panic. Ensure there is a request function before issuing
523 if (!q
->make_request_fn
)
526 bio
= bio_alloc(gfp_mask
, 0);
528 bio
->bi_opf
= REQ_OP_WRITE
| REQ_PREFLUSH
;
530 ret
= submit_bio_wait(bio
);
533 * The driver must store the error location in ->bi_sector, if
534 * it supports it. For non-stacked drivers, this should be
535 * copied from blk_rq_pos(rq).
538 *error_sector
= bio
->bi_iter
.bi_sector
;
543 EXPORT_SYMBOL(blkdev_issue_flush
);
545 struct blk_flush_queue
*blk_alloc_flush_queue(struct request_queue
*q
,
546 int node
, int cmd_size
)
548 struct blk_flush_queue
*fq
;
549 int rq_sz
= sizeof(struct request
);
551 fq
= kzalloc_node(sizeof(*fq
), GFP_KERNEL
, node
);
556 spin_lock_init(&fq
->mq_flush_lock
);
558 rq_sz
= round_up(rq_sz
+ cmd_size
, cache_line_size());
559 fq
->flush_rq
= kzalloc_node(rq_sz
, GFP_KERNEL
, node
);
563 INIT_LIST_HEAD(&fq
->flush_queue
[0]);
564 INIT_LIST_HEAD(&fq
->flush_queue
[1]);
565 INIT_LIST_HEAD(&fq
->flush_data_in_flight
);
575 void blk_free_flush_queue(struct blk_flush_queue
*fq
)
577 /* bio based request queue hasn't flush queue */