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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_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 * q->flush_queue[q->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
;
130 blk_clear_rq_complete(rq
);
133 static bool blk_flush_queue_rq(struct request
*rq
, bool add_front
)
136 struct request_queue
*q
= rq
->q
;
138 blk_mq_add_to_requeue_list(rq
, add_front
);
139 blk_mq_kick_requeue_list(q
);
143 list_add(&rq
->queuelist
, &rq
->q
->queue_head
);
145 list_add_tail(&rq
->queuelist
, &rq
->q
->queue_head
);
151 * blk_flush_complete_seq - complete flush sequence
152 * @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 q->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
, unsigned int seq
,
168 struct request_queue
*q
= rq
->q
;
169 struct list_head
*pending
= &q
->flush_queue
[q
->flush_pending_idx
];
170 bool queued
= false, kicked
;
172 BUG_ON(rq
->flush
.seq
& seq
);
173 rq
->flush
.seq
|= seq
;
176 seq
= blk_flush_cur_seq(rq
);
181 case REQ_FSEQ_PREFLUSH
:
182 case REQ_FSEQ_POSTFLUSH
:
183 /* queue for flush */
184 if (list_empty(pending
))
185 q
->flush_pending_since
= jiffies
;
186 list_move_tail(&rq
->flush
.list
, pending
);
190 list_move_tail(&rq
->flush
.list
, &q
->flush_data_in_flight
);
191 queued
= blk_flush_queue_rq(rq
, true);
196 * @rq was previously adjusted by blk_flush_issue() for
197 * flush sequencing and may already have gone through the
198 * flush data request completion path. Restore @rq for
199 * normal completion and end it.
201 BUG_ON(!list_empty(&rq
->queuelist
));
202 list_del_init(&rq
->flush
.list
);
203 blk_flush_restore_request(rq
);
205 blk_mq_end_io(rq
, error
);
207 __blk_end_request_all(rq
, error
);
214 kicked
= blk_kick_flush(q
);
215 return kicked
| queued
;
218 static void flush_end_io(struct request
*flush_rq
, int error
)
220 struct request_queue
*q
= flush_rq
->q
;
221 struct list_head
*running
;
223 struct request
*rq
, *n
;
224 unsigned long flags
= 0;
227 spin_lock_irqsave(&q
->mq_flush_lock
, flags
);
228 q
->flush_rq
->tag
= -1;
231 running
= &q
->flush_queue
[q
->flush_running_idx
];
232 BUG_ON(q
->flush_pending_idx
== q
->flush_running_idx
);
234 /* account completion of the flush request */
235 q
->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
|| q
->flush_queue_delayed
) {
261 blk_run_queue_async(q
);
263 q
->flush_queue_delayed
= 0;
265 spin_unlock_irqrestore(&q
->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 q->mq_flush_lock)
279 * %true if flush was issued, %false otherwise.
281 static bool blk_kick_flush(struct request_queue
*q
)
283 struct list_head
*pending
= &q
->flush_queue
[q
->flush_pending_idx
];
284 struct request
*first_rq
=
285 list_first_entry(pending
, struct request
, flush
.list
);
287 /* C1 described at the top of this file */
288 if (q
->flush_pending_idx
!= q
->flush_running_idx
|| list_empty(pending
))
292 if (!list_empty(&q
->flush_data_in_flight
) &&
294 q
->flush_pending_since
+ FLUSH_PENDING_TIMEOUT
))
298 * Issue flush and toggle pending_idx. This makes pending_idx
299 * different from running_idx, which means flush is in flight.
301 q
->flush_pending_idx
^= 1;
303 blk_rq_init(q
, q
->flush_rq
);
305 blk_mq_clone_flush_request(q
->flush_rq
, first_rq
);
307 q
->flush_rq
->cmd_type
= REQ_TYPE_FS
;
308 q
->flush_rq
->cmd_flags
= WRITE_FLUSH
| REQ_FLUSH_SEQ
;
309 q
->flush_rq
->rq_disk
= first_rq
->rq_disk
;
310 q
->flush_rq
->end_io
= flush_end_io
;
312 return blk_flush_queue_rq(q
->flush_rq
, false);
315 static void flush_data_end_io(struct request
*rq
, int error
)
317 struct request_queue
*q
= rq
->q
;
320 * After populating an empty queue, kick it to avoid stall. Read
321 * the comment in flush_end_io().
323 if (blk_flush_complete_seq(rq
, REQ_FSEQ_DATA
, error
))
324 blk_run_queue_async(q
);
327 static void mq_flush_data_end_io(struct request
*rq
, int error
)
329 struct request_queue
*q
= rq
->q
;
330 struct blk_mq_hw_ctx
*hctx
;
331 struct blk_mq_ctx
*ctx
;
335 hctx
= q
->mq_ops
->map_queue(q
, ctx
->cpu
);
338 * After populating an empty queue, kick it to avoid stall. Read
339 * the comment in flush_end_io().
341 spin_lock_irqsave(&q
->mq_flush_lock
, flags
);
342 if (blk_flush_complete_seq(rq
, REQ_FSEQ_DATA
, error
))
343 blk_mq_run_hw_queue(hctx
, true);
344 spin_unlock_irqrestore(&q
->mq_flush_lock
, flags
);
348 * blk_insert_flush - insert a new FLUSH/FUA request
349 * @rq: request to insert
351 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
352 * or __blk_mq_run_hw_queue() to dispatch request.
353 * @rq is being submitted. Analyze what needs to be done and put it on the
357 * spin_lock_irq(q->queue_lock) in !mq case
359 void blk_insert_flush(struct request
*rq
)
361 struct request_queue
*q
= rq
->q
;
362 unsigned int fflags
= q
->flush_flags
; /* may change, cache */
363 unsigned int policy
= blk_flush_policy(fflags
, rq
);
366 * @policy now records what operations need to be done. Adjust
367 * REQ_FLUSH and FUA for the driver.
369 rq
->cmd_flags
&= ~REQ_FLUSH
;
370 if (!(fflags
& REQ_FUA
))
371 rq
->cmd_flags
&= ~REQ_FUA
;
374 * An empty flush handed down from a stacking driver may
375 * translate into nothing if the underlying device does not
376 * advertise a write-back cache. In this case, simply
377 * complete the request.
381 blk_mq_end_io(rq
, 0);
383 __blk_end_bidi_request(rq
, 0, 0, 0);
387 BUG_ON(rq
->bio
!= rq
->biotail
); /*assumes zero or single bio rq */
390 * If there's data but flush is not necessary, the request can be
391 * processed directly without going through flush machinery. Queue
392 * for normal execution.
394 if ((policy
& REQ_FSEQ_DATA
) &&
395 !(policy
& (REQ_FSEQ_PREFLUSH
| REQ_FSEQ_POSTFLUSH
))) {
397 blk_mq_insert_request(rq
, false, false, true);
399 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
404 * @rq should go through flush machinery. Mark it part of flush
405 * sequence and submit for further processing.
407 memset(&rq
->flush
, 0, sizeof(rq
->flush
));
408 INIT_LIST_HEAD(&rq
->flush
.list
);
409 rq
->cmd_flags
|= REQ_FLUSH_SEQ
;
410 rq
->flush
.saved_end_io
= rq
->end_io
; /* Usually NULL */
412 rq
->end_io
= mq_flush_data_end_io
;
414 spin_lock_irq(&q
->mq_flush_lock
);
415 blk_flush_complete_seq(rq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
416 spin_unlock_irq(&q
->mq_flush_lock
);
419 rq
->end_io
= flush_data_end_io
;
421 blk_flush_complete_seq(rq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
425 * blkdev_issue_flush - queue a flush
426 * @bdev: blockdev to issue flush for
427 * @gfp_mask: memory allocation flags (for bio_alloc)
428 * @error_sector: error sector
431 * Issue a flush for the block device in question. Caller can supply
432 * room for storing the error offset in case of a flush error, if they
433 * wish to. If WAIT flag is not passed then caller may check only what
434 * request was pushed in some internal queue for later handling.
436 int blkdev_issue_flush(struct block_device
*bdev
, gfp_t gfp_mask
,
437 sector_t
*error_sector
)
439 struct request_queue
*q
;
443 if (bdev
->bd_disk
== NULL
)
446 q
= bdev_get_queue(bdev
);
451 * some block devices may not have their queue correctly set up here
452 * (e.g. loop device without a backing file) and so issuing a flush
453 * here will panic. Ensure there is a request function before issuing
456 if (!q
->make_request_fn
)
459 bio
= bio_alloc(gfp_mask
, 0);
462 ret
= submit_bio_wait(WRITE_FLUSH
, bio
);
465 * The driver must store the error location in ->bi_sector, if
466 * it supports it. For non-stacked drivers, this should be
467 * copied from blk_rq_pos(rq).
470 *error_sector
= bio
->bi_iter
.bi_sector
;
475 EXPORT_SYMBOL(blkdev_issue_flush
);
477 void blk_mq_init_flush(struct request_queue
*q
)
479 spin_lock_init(&q
->mq_flush_lock
);