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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 void 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 void blk_flush_queue_rq(struct request
*rq
, bool add_front
)
137 blk_mq_add_to_requeue_list(rq
, add_front
, true);
141 * blk_flush_complete_seq - complete flush sequence
142 * @rq: PREFLUSH/FUA request being sequenced
144 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
145 * @error: whether an error occurred
147 * @rq just completed @seq part of its flush sequence, record the
148 * completion and trigger the next step.
151 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
154 * %true if requests were added to the dispatch queue, %false otherwise.
156 static void blk_flush_complete_seq(struct request
*rq
,
157 struct blk_flush_queue
*fq
,
158 unsigned int seq
, blk_status_t error
)
160 struct request_queue
*q
= rq
->q
;
161 struct list_head
*pending
= &fq
->flush_queue
[fq
->flush_pending_idx
];
162 unsigned int cmd_flags
;
164 BUG_ON(rq
->flush
.seq
& seq
);
165 rq
->flush
.seq
|= seq
;
166 cmd_flags
= rq
->cmd_flags
;
169 seq
= blk_flush_cur_seq(rq
);
174 case REQ_FSEQ_PREFLUSH
:
175 case REQ_FSEQ_POSTFLUSH
:
176 /* queue for flush */
177 if (list_empty(pending
))
178 fq
->flush_pending_since
= jiffies
;
179 list_move_tail(&rq
->flush
.list
, pending
);
183 list_move_tail(&rq
->flush
.list
, &fq
->flush_data_in_flight
);
184 blk_flush_queue_rq(rq
, true);
189 * @rq was previously adjusted by blk_flush_issue() for
190 * flush sequencing and may already have gone through the
191 * flush data request completion path. Restore @rq for
192 * normal completion and end it.
194 BUG_ON(!list_empty(&rq
->queuelist
));
195 list_del_init(&rq
->flush
.list
);
196 blk_flush_restore_request(rq
);
197 blk_mq_end_request(rq
, error
);
204 blk_kick_flush(q
, fq
, cmd_flags
);
207 static void flush_end_io(struct request
*flush_rq
, blk_status_t error
)
209 struct request_queue
*q
= flush_rq
->q
;
210 struct list_head
*running
;
211 struct request
*rq
, *n
;
212 unsigned long flags
= 0;
213 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, flush_rq
->mq_ctx
);
214 struct blk_mq_hw_ctx
*hctx
;
216 /* release the tag's ownership to the req cloned from */
217 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
218 hctx
= blk_mq_map_queue(q
, flush_rq
->cmd_flags
, flush_rq
->mq_ctx
->cpu
);
220 blk_mq_tag_set_rq(hctx
, flush_rq
->tag
, fq
->orig_rq
);
223 blk_mq_put_driver_tag_hctx(hctx
, flush_rq
);
224 flush_rq
->internal_tag
= -1;
227 running
= &fq
->flush_queue
[fq
->flush_running_idx
];
228 BUG_ON(fq
->flush_pending_idx
== fq
->flush_running_idx
);
230 /* account completion of the flush request */
231 fq
->flush_running_idx
^= 1;
233 /* and push the waiting requests to the next stage */
234 list_for_each_entry_safe(rq
, n
, running
, flush
.list
) {
235 unsigned int seq
= blk_flush_cur_seq(rq
);
237 BUG_ON(seq
!= REQ_FSEQ_PREFLUSH
&& seq
!= REQ_FSEQ_POSTFLUSH
);
238 blk_flush_complete_seq(rq
, fq
, seq
, error
);
241 fq
->flush_queue_delayed
= 0;
242 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
246 * blk_kick_flush - consider issuing flush request
247 * @q: request_queue being kicked
249 * @flags: cmd_flags of the original request
251 * Flush related states of @q have changed, consider issuing flush request.
252 * Please read the comment at the top of this file for more info.
255 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
258 static void blk_kick_flush(struct request_queue
*q
, struct blk_flush_queue
*fq
,
261 struct list_head
*pending
= &fq
->flush_queue
[fq
->flush_pending_idx
];
262 struct request
*first_rq
=
263 list_first_entry(pending
, struct request
, flush
.list
);
264 struct request
*flush_rq
= fq
->flush_rq
;
265 struct blk_mq_hw_ctx
*hctx
;
267 /* C1 described at the top of this file */
268 if (fq
->flush_pending_idx
!= fq
->flush_running_idx
|| list_empty(pending
))
273 * For blk-mq + scheduling, we can risk having all driver tags
274 * assigned to empty flushes, and we deadlock if we are expecting
275 * other requests to make progress. Don't defer for that case.
277 if (!list_empty(&fq
->flush_data_in_flight
) &&
278 !(q
->mq_ops
&& q
->elevator
) &&
280 fq
->flush_pending_since
+ FLUSH_PENDING_TIMEOUT
))
284 * Issue flush and toggle pending_idx. This makes pending_idx
285 * different from running_idx, which means flush is in flight.
287 fq
->flush_pending_idx
^= 1;
289 blk_rq_init(q
, flush_rq
);
292 * In case of none scheduler, borrow tag from the first request
293 * since they can't be in flight at the same time. And acquire
294 * the tag's ownership for flush req.
296 * In case of IO scheduler, flush rq need to borrow scheduler tag
297 * just for cheating put/get driver tag.
299 flush_rq
->mq_ctx
= first_rq
->mq_ctx
;
302 fq
->orig_rq
= first_rq
;
303 flush_rq
->tag
= first_rq
->tag
;
304 hctx
= blk_mq_map_queue(q
, first_rq
->cmd_flags
,
305 first_rq
->mq_ctx
->cpu
);
306 blk_mq_tag_set_rq(hctx
, first_rq
->tag
, flush_rq
);
308 flush_rq
->internal_tag
= first_rq
->internal_tag
;
311 flush_rq
->cmd_flags
= REQ_OP_FLUSH
| REQ_PREFLUSH
;
312 flush_rq
->cmd_flags
|= (flags
& REQ_DRV
) | (flags
& REQ_FAILFAST_MASK
);
313 flush_rq
->rq_flags
|= RQF_FLUSH_SEQ
;
314 flush_rq
->rq_disk
= first_rq
->rq_disk
;
315 flush_rq
->end_io
= flush_end_io
;
317 blk_flush_queue_rq(flush_rq
, false);
320 static void mq_flush_data_end_io(struct request
*rq
, blk_status_t error
)
322 struct request_queue
*q
= rq
->q
;
323 struct blk_mq_hw_ctx
*hctx
;
324 struct blk_mq_ctx
*ctx
= rq
->mq_ctx
;
326 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, ctx
);
328 hctx
= blk_mq_map_queue(q
, rq
->cmd_flags
, ctx
->cpu
);
331 WARN_ON(rq
->tag
< 0);
332 blk_mq_put_driver_tag_hctx(hctx
, rq
);
336 * After populating an empty queue, kick it to avoid stall. Read
337 * the comment in flush_end_io().
339 spin_lock_irqsave(&fq
->mq_flush_lock
, flags
);
340 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_DATA
, error
);
341 spin_unlock_irqrestore(&fq
->mq_flush_lock
, flags
);
343 blk_mq_run_hw_queue(hctx
, true);
347 * blk_insert_flush - insert a new PREFLUSH/FUA request
348 * @rq: request to insert
350 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
351 * or __blk_mq_run_hw_queue() to dispatch request.
352 * @rq is being submitted. Analyze what needs to be done and put it on the
355 void blk_insert_flush(struct request
*rq
)
357 struct request_queue
*q
= rq
->q
;
358 unsigned long fflags
= q
->queue_flags
; /* may change, cache */
359 unsigned int policy
= blk_flush_policy(fflags
, rq
);
360 struct blk_flush_queue
*fq
= blk_get_flush_queue(q
, rq
->mq_ctx
);
363 * @policy now records what operations need to be done. Adjust
364 * REQ_PREFLUSH and FUA for the driver.
366 rq
->cmd_flags
&= ~REQ_PREFLUSH
;
367 if (!(fflags
& (1UL << QUEUE_FLAG_FUA
)))
368 rq
->cmd_flags
&= ~REQ_FUA
;
371 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
372 * of those flags, we have to set REQ_SYNC to avoid skewing
373 * the request accounting.
375 rq
->cmd_flags
|= REQ_SYNC
;
378 * An empty flush handed down from a stacking driver may
379 * translate into nothing if the underlying device does not
380 * advertise a write-back cache. In this case, simply
381 * complete the request.
384 blk_mq_end_request(rq
, 0);
388 BUG_ON(rq
->bio
!= rq
->biotail
); /*assumes zero or single bio rq */
391 * If there's data but flush is not necessary, the request can be
392 * processed directly without going through flush machinery. Queue
393 * for normal execution.
395 if ((policy
& REQ_FSEQ_DATA
) &&
396 !(policy
& (REQ_FSEQ_PREFLUSH
| REQ_FSEQ_POSTFLUSH
))) {
397 blk_mq_request_bypass_insert(rq
, false);
402 * @rq should go through flush machinery. Mark it part of flush
403 * sequence and submit for further processing.
405 memset(&rq
->flush
, 0, sizeof(rq
->flush
));
406 INIT_LIST_HEAD(&rq
->flush
.list
);
407 rq
->rq_flags
|= RQF_FLUSH_SEQ
;
408 rq
->flush
.saved_end_io
= rq
->end_io
; /* Usually NULL */
410 rq
->end_io
= mq_flush_data_end_io
;
412 spin_lock_irq(&fq
->mq_flush_lock
);
413 blk_flush_complete_seq(rq
, fq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
414 spin_unlock_irq(&fq
->mq_flush_lock
);
418 * blkdev_issue_flush - queue a flush
419 * @bdev: blockdev to issue flush for
420 * @gfp_mask: memory allocation flags (for bio_alloc)
421 * @error_sector: error sector
424 * Issue a flush for the block device in question. Caller can supply
425 * room for storing the error offset in case of a flush error, if they
428 int blkdev_issue_flush(struct block_device
*bdev
, gfp_t gfp_mask
,
429 sector_t
*error_sector
)
431 struct request_queue
*q
;
435 if (bdev
->bd_disk
== NULL
)
438 q
= bdev_get_queue(bdev
);
443 * some block devices may not have their queue correctly set up here
444 * (e.g. loop device without a backing file) and so issuing a flush
445 * here will panic. Ensure there is a request function before issuing
448 if (!q
->make_request_fn
)
451 bio
= bio_alloc(gfp_mask
, 0);
452 bio_set_dev(bio
, bdev
);
453 bio
->bi_opf
= REQ_OP_WRITE
| REQ_PREFLUSH
;
455 ret
= submit_bio_wait(bio
);
458 * The driver must store the error location in ->bi_sector, if
459 * it supports it. For non-stacked drivers, this should be
460 * copied from blk_rq_pos(rq).
463 *error_sector
= bio
->bi_iter
.bi_sector
;
468 EXPORT_SYMBOL(blkdev_issue_flush
);
470 struct blk_flush_queue
*blk_alloc_flush_queue(struct request_queue
*q
,
471 int node
, int cmd_size
, gfp_t flags
)
473 struct blk_flush_queue
*fq
;
474 int rq_sz
= sizeof(struct request
);
476 fq
= kzalloc_node(sizeof(*fq
), flags
, node
);
480 spin_lock_init(&fq
->mq_flush_lock
);
482 rq_sz
= round_up(rq_sz
+ cmd_size
, cache_line_size());
483 fq
->flush_rq
= kzalloc_node(rq_sz
, flags
, node
);
487 INIT_LIST_HEAD(&fq
->flush_queue
[0]);
488 INIT_LIST_HEAD(&fq
->flush_queue
[1]);
489 INIT_LIST_HEAD(&fq
->flush_data_in_flight
);
499 void blk_free_flush_queue(struct blk_flush_queue
*fq
)
501 /* bio based request queue hasn't flush queue */