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1/*
2 * Functions to sequence PREFLUSH and FUA writes.
3 *
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
6 *
7 * This file is released under the GPLv2.
8 *
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.
12 *
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
17 * completion.
18 *
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.
22 *
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.
25 *
26 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
27 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
28 *
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
35 * requests.
36 *
37 * Currently, the following conditions are used to determine when to issue
38 * flush.
39 *
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
42 *
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
45 * PREFLUSH.
46 *
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.
51 *
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
53 * is beneficial.
54 *
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
60 * req_bio_endio().
61 *
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.
65 */
66
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>
73
74#include "blk.h"
75#include "blk-mq.h"
76#include "blk-mq-tag.h"
77#include "blk-mq-sched.h"
78
79/* PREFLUSH/FUA sequences */
80enum {
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),
85
86 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
87 REQ_FSEQ_POSTFLUSH,
88
89 /*
90 * If flush has been pending longer than the following timeout,
91 * it's issued even if flush_data requests are still in flight.
92 */
93 FLUSH_PENDING_TIMEOUT = 5 * HZ,
94};
95
96static bool blk_kick_flush(struct request_queue *q,
97 struct blk_flush_queue *fq);
98
99static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
100{
101 unsigned int policy = 0;
102
103 if (blk_rq_sectors(rq))
104 policy |= REQ_FSEQ_DATA;
105
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;
112 }
113 return policy;
114}
115
116static unsigned int blk_flush_cur_seq(struct request *rq)
117{
118 return 1 << ffz(rq->flush.seq);
119}
120
121static void blk_flush_restore_request(struct request *rq)
122{
123 /*
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.
127 */
128 rq->bio = rq->biotail;
129
130 /* make @rq a normal request */
131 rq->rq_flags &= ~RQF_FLUSH_SEQ;
132 rq->end_io = rq->flush.saved_end_io;
133}
134
135static bool blk_flush_queue_rq(struct request *rq, bool add_front)
136{
137 if (rq->q->mq_ops) {
138 blk_mq_add_to_requeue_list(rq, add_front, true);
139 return false;
140 } else {
141 if (add_front)
142 list_add(&rq->queuelist, &rq->q->queue_head);
143 else
144 list_add_tail(&rq->queuelist, &rq->q->queue_head);
145 return true;
146 }
147}
148
149/**
150 * blk_flush_complete_seq - complete flush sequence
151 * @rq: PREFLUSH/FUA request being sequenced
152 * @fq: flush queue
153 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
154 * @error: whether an error occurred
155 *
156 * @rq just completed @seq part of its flush sequence, record the
157 * completion and trigger the next step.
158 *
159 * CONTEXT:
160 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
161 *
162 * RETURNS:
163 * %true if requests were added to the dispatch queue, %false otherwise.
164 */
165static bool blk_flush_complete_seq(struct request *rq,
166 struct blk_flush_queue *fq,
167 unsigned int seq, blk_status_t error)
168{
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
173 BUG_ON(rq->flush.seq & seq);
174 rq->flush.seq |= seq;
175
176 if (likely(!error))
177 seq = blk_flush_cur_seq(rq);
178 else
179 seq = REQ_FSEQ_DONE;
180
181 switch (seq) {
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);
188 break;
189
190 case REQ_FSEQ_DATA:
191 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
192 queued = blk_flush_queue_rq(rq, true);
193 break;
194
195 case REQ_FSEQ_DONE:
196 /*
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.
201 */
202 BUG_ON(!list_empty(&rq->queuelist));
203 list_del_init(&rq->flush.list);
204 blk_flush_restore_request(rq);
205 if (q->mq_ops)
206 blk_mq_end_request(rq, error);
207 else
208 __blk_end_request_all(rq, error);
209 break;
210
211 default:
212 BUG();
213 }
214
215 kicked = blk_kick_flush(q, fq);
216 return kicked | queued;
217}
218
219static void flush_end_io(struct request *flush_rq, blk_status_t error)
220{
221 struct request_queue *q = flush_rq->q;
222 struct list_head *running;
223 bool queued = false;
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);
227
228 if (q->mq_ops) {
229 struct blk_mq_hw_ctx *hctx;
230
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 if (!q->elevator) {
235 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
236 flush_rq->tag = -1;
237 } else {
238 blk_mq_put_driver_tag_hctx(hctx, flush_rq);
239 flush_rq->internal_tag = -1;
240 }
241 }
242
243 running = &fq->flush_queue[fq->flush_running_idx];
244 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
245
246 /* account completion of the flush request */
247 fq->flush_running_idx ^= 1;
248
249 if (!q->mq_ops)
250 elv_completed_request(q, flush_rq);
251
252 /* and push the waiting requests to the next stage */
253 list_for_each_entry_safe(rq, n, running, flush.list) {
254 unsigned int seq = blk_flush_cur_seq(rq);
255
256 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
257 queued |= blk_flush_complete_seq(rq, fq, seq, error);
258 }
259
260 /*
261 * Kick the queue to avoid stall for two cases:
262 * 1. Moving a request silently to empty queue_head may stall the
263 * queue.
264 * 2. When flush request is running in non-queueable queue, the
265 * queue is hold. Restart the queue after flush request is finished
266 * to avoid stall.
267 * This function is called from request completion path and calling
268 * directly into request_fn may confuse the driver. Always use
269 * kblockd.
270 */
271 if (queued || fq->flush_queue_delayed) {
272 WARN_ON(q->mq_ops);
273 blk_run_queue_async(q);
274 }
275 fq->flush_queue_delayed = 0;
276 if (q->mq_ops)
277 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
278}
279
280/**
281 * blk_kick_flush - consider issuing flush request
282 * @q: request_queue being kicked
283 * @fq: flush queue
284 *
285 * Flush related states of @q have changed, consider issuing flush request.
286 * Please read the comment at the top of this file for more info.
287 *
288 * CONTEXT:
289 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
290 *
291 * RETURNS:
292 * %true if flush was issued, %false otherwise.
293 */
294static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
295{
296 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
297 struct request *first_rq =
298 list_first_entry(pending, struct request, flush.list);
299 struct request *flush_rq = fq->flush_rq;
300
301 /* C1 described at the top of this file */
302 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
303 return false;
304
305 /* C2 and C3
306 *
307 * For blk-mq + scheduling, we can risk having all driver tags
308 * assigned to empty flushes, and we deadlock if we are expecting
309 * other requests to make progress. Don't defer for that case.
310 */
311 if (!list_empty(&fq->flush_data_in_flight) &&
312 !(q->mq_ops && q->elevator) &&
313 time_before(jiffies,
314 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
315 return false;
316
317 /*
318 * Issue flush and toggle pending_idx. This makes pending_idx
319 * different from running_idx, which means flush is in flight.
320 */
321 fq->flush_pending_idx ^= 1;
322
323 blk_rq_init(q, flush_rq);
324
325 /*
326 * In case of none scheduler, borrow tag from the first request
327 * since they can't be in flight at the same time. And acquire
328 * the tag's ownership for flush req.
329 *
330 * In case of IO scheduler, flush rq need to borrow scheduler tag
331 * just for cheating put/get driver tag.
332 */
333 if (q->mq_ops) {
334 struct blk_mq_hw_ctx *hctx;
335
336 flush_rq->mq_ctx = first_rq->mq_ctx;
337
338 if (!q->elevator) {
339 fq->orig_rq = first_rq;
340 flush_rq->tag = first_rq->tag;
341 hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
342 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
343 } else {
344 flush_rq->internal_tag = first_rq->internal_tag;
345 }
346 }
347
348 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
349 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
350 flush_rq->rq_disk = first_rq->rq_disk;
351 flush_rq->end_io = flush_end_io;
352
353 return blk_flush_queue_rq(flush_rq, false);
354}
355
356static void flush_data_end_io(struct request *rq, blk_status_t error)
357{
358 struct request_queue *q = rq->q;
359 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
360
361 lockdep_assert_held(q->queue_lock);
362
363 /*
364 * Updating q->in_flight[] here for making this tag usable
365 * early. Because in blk_queue_start_tag(),
366 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
367 * reserve tags for sync I/O.
368 *
369 * More importantly this way can avoid the following I/O
370 * deadlock:
371 *
372 * - suppose there are 40 fua requests comming to flush queue
373 * and queue depth is 31
374 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
375 * tag for async I/O any more
376 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
377 * and flush_data_end_io() is called
378 * - the other rqs still can't go ahead if not updating
379 * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
380 * are held in flush data queue and make no progress of
381 * handling post flush rq
382 * - only after the post flush rq is handled, all these rqs
383 * can be completed
384 */
385
386 elv_completed_request(q, rq);
387
388 /* for avoiding double accounting */
389 rq->rq_flags &= ~RQF_STARTED;
390
391 /*
392 * After populating an empty queue, kick it to avoid stall. Read
393 * the comment in flush_end_io().
394 */
395 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
396 blk_run_queue_async(q);
397}
398
399static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
400{
401 struct request_queue *q = rq->q;
402 struct blk_mq_hw_ctx *hctx;
403 struct blk_mq_ctx *ctx = rq->mq_ctx;
404 unsigned long flags;
405 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
406
407 hctx = blk_mq_map_queue(q, ctx->cpu);
408
409 if (q->elevator) {
410 WARN_ON(rq->tag < 0);
411 blk_mq_put_driver_tag_hctx(hctx, rq);
412 }
413
414 /*
415 * After populating an empty queue, kick it to avoid stall. Read
416 * the comment in flush_end_io().
417 */
418 spin_lock_irqsave(&fq->mq_flush_lock, flags);
419 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
420 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
421
422 blk_mq_run_hw_queue(hctx, true);
423}
424
425/**
426 * blk_insert_flush - insert a new PREFLUSH/FUA request
427 * @rq: request to insert
428 *
429 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
430 * or __blk_mq_run_hw_queue() to dispatch request.
431 * @rq is being submitted. Analyze what needs to be done and put it on the
432 * right queue.
433 */
434void blk_insert_flush(struct request *rq)
435{
436 struct request_queue *q = rq->q;
437 unsigned long fflags = q->queue_flags; /* may change, cache */
438 unsigned int policy = blk_flush_policy(fflags, rq);
439 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
440
441 if (!q->mq_ops)
442 lockdep_assert_held(q->queue_lock);
443
444 /*
445 * @policy now records what operations need to be done. Adjust
446 * REQ_PREFLUSH and FUA for the driver.
447 */
448 rq->cmd_flags &= ~REQ_PREFLUSH;
449 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
450 rq->cmd_flags &= ~REQ_FUA;
451
452 /*
453 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
454 * of those flags, we have to set REQ_SYNC to avoid skewing
455 * the request accounting.
456 */
457 rq->cmd_flags |= REQ_SYNC;
458
459 /*
460 * An empty flush handed down from a stacking driver may
461 * translate into nothing if the underlying device does not
462 * advertise a write-back cache. In this case, simply
463 * complete the request.
464 */
465 if (!policy) {
466 if (q->mq_ops)
467 blk_mq_end_request(rq, 0);
468 else
469 __blk_end_request(rq, 0, 0);
470 return;
471 }
472
473 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
474
475 /*
476 * If there's data but flush is not necessary, the request can be
477 * processed directly without going through flush machinery. Queue
478 * for normal execution.
479 */
480 if ((policy & REQ_FSEQ_DATA) &&
481 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
482 if (q->mq_ops)
483 blk_mq_request_bypass_insert(rq, false);
484 else
485 list_add_tail(&rq->queuelist, &q->queue_head);
486 return;
487 }
488
489 /*
490 * @rq should go through flush machinery. Mark it part of flush
491 * sequence and submit for further processing.
492 */
493 memset(&rq->flush, 0, sizeof(rq->flush));
494 INIT_LIST_HEAD(&rq->flush.list);
495 rq->rq_flags |= RQF_FLUSH_SEQ;
496 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
497 if (q->mq_ops) {
498 rq->end_io = mq_flush_data_end_io;
499
500 spin_lock_irq(&fq->mq_flush_lock);
501 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
502 spin_unlock_irq(&fq->mq_flush_lock);
503 return;
504 }
505 rq->end_io = flush_data_end_io;
506
507 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
508}
509
510/**
511 * blkdev_issue_flush - queue a flush
512 * @bdev: blockdev to issue flush for
513 * @gfp_mask: memory allocation flags (for bio_alloc)
514 * @error_sector: error sector
515 *
516 * Description:
517 * Issue a flush for the block device in question. Caller can supply
518 * room for storing the error offset in case of a flush error, if they
519 * wish to.
520 */
521int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
522 sector_t *error_sector)
523{
524 struct request_queue *q;
525 struct bio *bio;
526 int ret = 0;
527
528 if (bdev->bd_disk == NULL)
529 return -ENXIO;
530
531 q = bdev_get_queue(bdev);
532 if (!q)
533 return -ENXIO;
534
535 /*
536 * some block devices may not have their queue correctly set up here
537 * (e.g. loop device without a backing file) and so issuing a flush
538 * here will panic. Ensure there is a request function before issuing
539 * the flush.
540 */
541 if (!q->make_request_fn)
542 return -ENXIO;
543
544 bio = bio_alloc(gfp_mask, 0);
545 bio_set_dev(bio, bdev);
546 bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
547
548 ret = submit_bio_wait(bio);
549
550 /*
551 * The driver must store the error location in ->bi_sector, if
552 * it supports it. For non-stacked drivers, this should be
553 * copied from blk_rq_pos(rq).
554 */
555 if (error_sector)
556 *error_sector = bio->bi_iter.bi_sector;
557
558 bio_put(bio);
559 return ret;
560}
561EXPORT_SYMBOL(blkdev_issue_flush);
562
563struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
564 int node, int cmd_size)
565{
566 struct blk_flush_queue *fq;
567 int rq_sz = sizeof(struct request);
568
569 fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
570 if (!fq)
571 goto fail;
572
573 if (q->mq_ops)
574 spin_lock_init(&fq->mq_flush_lock);
575
576 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
577 fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
578 if (!fq->flush_rq)
579 goto fail_rq;
580
581 INIT_LIST_HEAD(&fq->flush_queue[0]);
582 INIT_LIST_HEAD(&fq->flush_queue[1]);
583 INIT_LIST_HEAD(&fq->flush_data_in_flight);
584
585 return fq;
586
587 fail_rq:
588 kfree(fq);
589 fail:
590 return NULL;
591}
592
593void blk_free_flush_queue(struct blk_flush_queue *fq)
594{
595 /* bio based request queue hasn't flush queue */
596 if (!fq)
597 return;
598
599 kfree(fq->flush_rq);
600 kfree(fq);
601}
1/*
2 * Functions to sequence FLUSH and FUA writes.
3 *
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
6 *
7 * This file is released under the GPLv2.
8 *
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.
12 *
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
17 * completion.
18 *
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.
22 *
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.
25 *
26 * If the device has writeback cache and doesn't support FUA, REQ_FLUSH is
27 * translated to PREFLUSH and REQ_FUA to POSTFLUSH.
28 *
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
35 * requests.
36 *
37 * Currently, the following conditions are used to determine when to issue
38 * flush.
39 *
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
42 *
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
45 * PREFLUSH.
46 *
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.
51 *
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
53 * is beneficial.
54 *
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
60 * req_bio_endio().
61 *
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.
65 */
66
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>
73
74#include "blk.h"
75#include "blk-mq.h"
76#include "blk-mq-tag.h"
77
78/* FLUSH/FUA sequences */
79enum {
80 REQ_FSEQ_PREFLUSH = (1 << 0), /* pre-flushing in progress */
81 REQ_FSEQ_DATA = (1 << 1), /* data write in progress */
82 REQ_FSEQ_POSTFLUSH = (1 << 2), /* post-flushing in progress */
83 REQ_FSEQ_DONE = (1 << 3),
84
85 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
86 REQ_FSEQ_POSTFLUSH,
87
88 /*
89 * If flush has been pending longer than the following timeout,
90 * it's issued even if flush_data requests are still in flight.
91 */
92 FLUSH_PENDING_TIMEOUT = 5 * HZ,
93};
94
95static bool blk_kick_flush(struct request_queue *q,
96 struct blk_flush_queue *fq);
97
98static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
99{
100 unsigned int policy = 0;
101
102 if (blk_rq_sectors(rq))
103 policy |= REQ_FSEQ_DATA;
104
105 if (fflags & REQ_FLUSH) {
106 if (rq->cmd_flags & REQ_FLUSH)
107 policy |= REQ_FSEQ_PREFLUSH;
108 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
109 policy |= REQ_FSEQ_POSTFLUSH;
110 }
111 return policy;
112}
113
114static unsigned int blk_flush_cur_seq(struct request *rq)
115{
116 return 1 << ffz(rq->flush.seq);
117}
118
119static void blk_flush_restore_request(struct request *rq)
120{
121 /*
122 * After flush data completion, @rq->bio is %NULL but we need to
123 * complete the bio again. @rq->biotail is guaranteed to equal the
124 * original @rq->bio. Restore it.
125 */
126 rq->bio = rq->biotail;
127
128 /* make @rq a normal request */
129 rq->cmd_flags &= ~REQ_FLUSH_SEQ;
130 rq->end_io = rq->flush.saved_end_io;
131}
132
133static bool blk_flush_queue_rq(struct request *rq, bool add_front)
134{
135 if (rq->q->mq_ops) {
136 struct request_queue *q = rq->q;
137
138 blk_mq_add_to_requeue_list(rq, add_front);
139 blk_mq_kick_requeue_list(q);
140 return false;
141 } else {
142 if (add_front)
143 list_add(&rq->queuelist, &rq->q->queue_head);
144 else
145 list_add_tail(&rq->queuelist, &rq->q->queue_head);
146 return true;
147 }
148}
149
150/**
151 * blk_flush_complete_seq - complete flush sequence
152 * @rq: FLUSH/FUA request being sequenced
153 * @fq: flush queue
154 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
155 * @error: whether an error occurred
156 *
157 * @rq just completed @seq part of its flush sequence, record the
158 * completion and trigger the next step.
159 *
160 * CONTEXT:
161 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
162 *
163 * RETURNS:
164 * %true if requests were added to the dispatch queue, %false otherwise.
165 */
166static bool blk_flush_complete_seq(struct request *rq,
167 struct blk_flush_queue *fq,
168 unsigned int seq, int error)
169{
170 struct request_queue *q = rq->q;
171 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
172 bool queued = false, kicked;
173
174 BUG_ON(rq->flush.seq & seq);
175 rq->flush.seq |= seq;
176
177 if (likely(!error))
178 seq = blk_flush_cur_seq(rq);
179 else
180 seq = REQ_FSEQ_DONE;
181
182 switch (seq) {
183 case REQ_FSEQ_PREFLUSH:
184 case REQ_FSEQ_POSTFLUSH:
185 /* queue for flush */
186 if (list_empty(pending))
187 fq->flush_pending_since = jiffies;
188 list_move_tail(&rq->flush.list, pending);
189 break;
190
191 case REQ_FSEQ_DATA:
192 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
193 queued = blk_flush_queue_rq(rq, true);
194 break;
195
196 case REQ_FSEQ_DONE:
197 /*
198 * @rq was previously adjusted by blk_flush_issue() for
199 * flush sequencing and may already have gone through the
200 * flush data request completion path. Restore @rq for
201 * normal completion and end it.
202 */
203 BUG_ON(!list_empty(&rq->queuelist));
204 list_del_init(&rq->flush.list);
205 blk_flush_restore_request(rq);
206 if (q->mq_ops)
207 blk_mq_end_request(rq, error);
208 else
209 __blk_end_request_all(rq, error);
210 break;
211
212 default:
213 BUG();
214 }
215
216 kicked = blk_kick_flush(q, fq);
217 return kicked | queued;
218}
219
220static void flush_end_io(struct request *flush_rq, int error)
221{
222 struct request_queue *q = flush_rq->q;
223 struct list_head *running;
224 bool queued = false;
225 struct request *rq, *n;
226 unsigned long flags = 0;
227 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
228
229 if (q->mq_ops) {
230 struct blk_mq_hw_ctx *hctx;
231
232 /* release the tag's ownership to the req cloned from */
233 spin_lock_irqsave(&fq->mq_flush_lock, flags);
234 hctx = q->mq_ops->map_queue(q, flush_rq->mq_ctx->cpu);
235 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
236 flush_rq->tag = -1;
237 }
238
239 running = &fq->flush_queue[fq->flush_running_idx];
240 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
241
242 /* account completion of the flush request */
243 fq->flush_running_idx ^= 1;
244
245 if (!q->mq_ops)
246 elv_completed_request(q, flush_rq);
247
248 /* and push the waiting requests to the next stage */
249 list_for_each_entry_safe(rq, n, running, flush.list) {
250 unsigned int seq = blk_flush_cur_seq(rq);
251
252 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
253 queued |= blk_flush_complete_seq(rq, fq, seq, error);
254 }
255
256 /*
257 * Kick the queue to avoid stall for two cases:
258 * 1. Moving a request silently to empty queue_head may stall the
259 * queue.
260 * 2. When flush request is running in non-queueable queue, the
261 * queue is hold. Restart the queue after flush request is finished
262 * to avoid stall.
263 * This function is called from request completion path and calling
264 * directly into request_fn may confuse the driver. Always use
265 * kblockd.
266 */
267 if (queued || fq->flush_queue_delayed) {
268 WARN_ON(q->mq_ops);
269 blk_run_queue_async(q);
270 }
271 fq->flush_queue_delayed = 0;
272 if (q->mq_ops)
273 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
274}
275
276/**
277 * blk_kick_flush - consider issuing flush request
278 * @q: request_queue being kicked
279 * @fq: flush queue
280 *
281 * Flush related states of @q have changed, consider issuing flush request.
282 * Please read the comment at the top of this file for more info.
283 *
284 * CONTEXT:
285 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
286 *
287 * RETURNS:
288 * %true if flush was issued, %false otherwise.
289 */
290static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
291{
292 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
293 struct request *first_rq =
294 list_first_entry(pending, struct request, flush.list);
295 struct request *flush_rq = fq->flush_rq;
296
297 /* C1 described at the top of this file */
298 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
299 return false;
300
301 /* C2 and C3 */
302 if (!list_empty(&fq->flush_data_in_flight) &&
303 time_before(jiffies,
304 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
305 return false;
306
307 /*
308 * Issue flush and toggle pending_idx. This makes pending_idx
309 * different from running_idx, which means flush is in flight.
310 */
311 fq->flush_pending_idx ^= 1;
312
313 blk_rq_init(q, flush_rq);
314
315 /*
316 * Borrow tag from the first request since they can't
317 * be in flight at the same time. And acquire the tag's
318 * ownership for flush req.
319 */
320 if (q->mq_ops) {
321 struct blk_mq_hw_ctx *hctx;
322
323 flush_rq->mq_ctx = first_rq->mq_ctx;
324 flush_rq->tag = first_rq->tag;
325 fq->orig_rq = first_rq;
326
327 hctx = q->mq_ops->map_queue(q, first_rq->mq_ctx->cpu);
328 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
329 }
330
331 flush_rq->cmd_type = REQ_TYPE_FS;
332 flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
333 flush_rq->rq_disk = first_rq->rq_disk;
334 flush_rq->end_io = flush_end_io;
335
336 return blk_flush_queue_rq(flush_rq, false);
337}
338
339static void flush_data_end_io(struct request *rq, int error)
340{
341 struct request_queue *q = rq->q;
342 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
343
344 /*
345 * After populating an empty queue, kick it to avoid stall. Read
346 * the comment in flush_end_io().
347 */
348 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
349 blk_run_queue_async(q);
350}
351
352static void mq_flush_data_end_io(struct request *rq, int error)
353{
354 struct request_queue *q = rq->q;
355 struct blk_mq_hw_ctx *hctx;
356 struct blk_mq_ctx *ctx = rq->mq_ctx;
357 unsigned long flags;
358 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
359
360 hctx = q->mq_ops->map_queue(q, ctx->cpu);
361
362 /*
363 * After populating an empty queue, kick it to avoid stall. Read
364 * the comment in flush_end_io().
365 */
366 spin_lock_irqsave(&fq->mq_flush_lock, flags);
367 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
368 blk_mq_run_hw_queue(hctx, true);
369 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
370}
371
372/**
373 * blk_insert_flush - insert a new FLUSH/FUA request
374 * @rq: request to insert
375 *
376 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
377 * or __blk_mq_run_hw_queue() to dispatch request.
378 * @rq is being submitted. Analyze what needs to be done and put it on the
379 * right queue.
380 *
381 * CONTEXT:
382 * spin_lock_irq(q->queue_lock) in !mq case
383 */
384void blk_insert_flush(struct request *rq)
385{
386 struct request_queue *q = rq->q;
387 unsigned int fflags = q->flush_flags; /* may change, cache */
388 unsigned int policy = blk_flush_policy(fflags, rq);
389 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
390
391 /*
392 * @policy now records what operations need to be done. Adjust
393 * REQ_FLUSH and FUA for the driver.
394 */
395 rq->cmd_flags &= ~REQ_FLUSH;
396 if (!(fflags & REQ_FUA))
397 rq->cmd_flags &= ~REQ_FUA;
398
399 /*
400 * An empty flush handed down from a stacking driver may
401 * translate into nothing if the underlying device does not
402 * advertise a write-back cache. In this case, simply
403 * complete the request.
404 */
405 if (!policy) {
406 if (q->mq_ops)
407 blk_mq_end_request(rq, 0);
408 else
409 __blk_end_bidi_request(rq, 0, 0, 0);
410 return;
411 }
412
413 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
414
415 /*
416 * If there's data but flush is not necessary, the request can be
417 * processed directly without going through flush machinery. Queue
418 * for normal execution.
419 */
420 if ((policy & REQ_FSEQ_DATA) &&
421 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
422 if (q->mq_ops) {
423 blk_mq_insert_request(rq, false, false, true);
424 } else
425 list_add_tail(&rq->queuelist, &q->queue_head);
426 return;
427 }
428
429 /*
430 * @rq should go through flush machinery. Mark it part of flush
431 * sequence and submit for further processing.
432 */
433 memset(&rq->flush, 0, sizeof(rq->flush));
434 INIT_LIST_HEAD(&rq->flush.list);
435 rq->cmd_flags |= REQ_FLUSH_SEQ;
436 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
437 if (q->mq_ops) {
438 rq->end_io = mq_flush_data_end_io;
439
440 spin_lock_irq(&fq->mq_flush_lock);
441 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
442 spin_unlock_irq(&fq->mq_flush_lock);
443 return;
444 }
445 rq->end_io = flush_data_end_io;
446
447 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
448}
449
450/**
451 * blkdev_issue_flush - queue a flush
452 * @bdev: blockdev to issue flush for
453 * @gfp_mask: memory allocation flags (for bio_alloc)
454 * @error_sector: error sector
455 *
456 * Description:
457 * Issue a flush for the block device in question. Caller can supply
458 * room for storing the error offset in case of a flush error, if they
459 * wish to. If WAIT flag is not passed then caller may check only what
460 * request was pushed in some internal queue for later handling.
461 */
462int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
463 sector_t *error_sector)
464{
465 struct request_queue *q;
466 struct bio *bio;
467 int ret = 0;
468
469 if (bdev->bd_disk == NULL)
470 return -ENXIO;
471
472 q = bdev_get_queue(bdev);
473 if (!q)
474 return -ENXIO;
475
476 /*
477 * some block devices may not have their queue correctly set up here
478 * (e.g. loop device without a backing file) and so issuing a flush
479 * here will panic. Ensure there is a request function before issuing
480 * the flush.
481 */
482 if (!q->make_request_fn)
483 return -ENXIO;
484
485 bio = bio_alloc(gfp_mask, 0);
486 bio->bi_bdev = bdev;
487
488 ret = submit_bio_wait(WRITE_FLUSH, bio);
489
490 /*
491 * The driver must store the error location in ->bi_sector, if
492 * it supports it. For non-stacked drivers, this should be
493 * copied from blk_rq_pos(rq).
494 */
495 if (error_sector)
496 *error_sector = bio->bi_iter.bi_sector;
497
498 bio_put(bio);
499 return ret;
500}
501EXPORT_SYMBOL(blkdev_issue_flush);
502
503struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
504 int node, int cmd_size)
505{
506 struct blk_flush_queue *fq;
507 int rq_sz = sizeof(struct request);
508
509 fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
510 if (!fq)
511 goto fail;
512
513 if (q->mq_ops) {
514 spin_lock_init(&fq->mq_flush_lock);
515 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
516 }
517
518 fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
519 if (!fq->flush_rq)
520 goto fail_rq;
521
522 INIT_LIST_HEAD(&fq->flush_queue[0]);
523 INIT_LIST_HEAD(&fq->flush_queue[1]);
524 INIT_LIST_HEAD(&fq->flush_data_in_flight);
525
526 return fq;
527
528 fail_rq:
529 kfree(fq);
530 fail:
531 return NULL;
532}
533
534void blk_free_flush_queue(struct blk_flush_queue *fq)
535{
536 /* bio based request queue hasn't flush queue */
537 if (!fq)
538 return;
539
540 kfree(fq->flush_rq);
541 kfree(fq);
542}