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1// SPDX-License-Identifier: GPL-2.0
2/*
3 * Functions to sequence PREFLUSH and FUA writes.
4 *
5 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
6 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
7 *
8 * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
9 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
10 * properties and hardware capability.
11 *
12 * If a request doesn't have data, only REQ_PREFLUSH makes sense, which
13 * indicates a simple flush request. If there is data, REQ_PREFLUSH indicates
14 * that the device cache should be flushed before the data is executed, and
15 * REQ_FUA means that the data must be on non-volatile media on request
16 * completion.
17 *
18 * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
19 * difference. The requests are either completed immediately if there's no data
20 * or executed as normal requests otherwise.
21 *
22 * If the device has writeback cache and supports FUA, REQ_PREFLUSH is
23 * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
24 *
25 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
26 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
27 *
28 * The actual execution of flush is double buffered. Whenever a request
29 * needs to execute PRE or POSTFLUSH, it queues at
30 * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a
31 * REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush
32 * completes, all the requests which were pending are proceeded to the next
33 * step. This allows arbitrary merging of different types of PREFLUSH/FUA
34 * requests.
35 *
36 * Currently, the following conditions are used to determine when to issue
37 * flush.
38 *
39 * C1. At any given time, only one flush shall be in progress. This makes
40 * double buffering sufficient.
41 *
42 * C2. Flush is deferred if any request is executing DATA of its sequence.
43 * This avoids issuing separate POSTFLUSHes for requests which shared
44 * PREFLUSH.
45 *
46 * C3. The second condition is ignored if there is a request which has
47 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid
48 * starvation in the unlikely case where there are continuous stream of
49 * FUA (without PREFLUSH) requests.
50 *
51 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
52 * is beneficial.
53 *
54 * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
55 * Once while executing DATA and again after the whole sequence is
56 * complete. The first completion updates the contained bio but doesn't
57 * finish it so that the bio submitter is notified only after the whole
58 * sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in
59 * req_bio_endio().
60 *
61 * The above peculiarity requires that each PREFLUSH/FUA request has only one
62 * bio attached to it, which is guaranteed as they aren't allowed to be
63 * merged in the usual way.
64 */
65
66#include <linux/kernel.h>
67#include <linux/module.h>
68#include <linux/bio.h>
69#include <linux/blkdev.h>
70#include <linux/gfp.h>
71#include <linux/blk-mq.h>
72#include <linux/part_stat.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 void blk_kick_flush(struct request_queue *q,
97 struct blk_flush_queue *fq, blk_opf_t flags);
98
99static inline struct blk_flush_queue *
100blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
101{
102 return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
103}
104
105static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
106{
107 unsigned int policy = 0;
108
109 if (blk_rq_sectors(rq))
110 policy |= REQ_FSEQ_DATA;
111
112 if (fflags & (1UL << QUEUE_FLAG_WC)) {
113 if (rq->cmd_flags & REQ_PREFLUSH)
114 policy |= REQ_FSEQ_PREFLUSH;
115 if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
116 (rq->cmd_flags & REQ_FUA))
117 policy |= REQ_FSEQ_POSTFLUSH;
118 }
119 return policy;
120}
121
122static unsigned int blk_flush_cur_seq(struct request *rq)
123{
124 return 1 << ffz(rq->flush.seq);
125}
126
127static void blk_flush_restore_request(struct request *rq)
128{
129 /*
130 * After flush data completion, @rq->bio is %NULL but we need to
131 * complete the bio again. @rq->biotail is guaranteed to equal the
132 * original @rq->bio. Restore it.
133 */
134 rq->bio = rq->biotail;
135
136 /* make @rq a normal request */
137 rq->rq_flags &= ~RQF_FLUSH_SEQ;
138 rq->end_io = rq->flush.saved_end_io;
139}
140
141static void blk_flush_queue_rq(struct request *rq, bool add_front)
142{
143 blk_mq_add_to_requeue_list(rq, add_front, true);
144}
145
146static void blk_account_io_flush(struct request *rq)
147{
148 struct block_device *part = rq->q->disk->part0;
149
150 part_stat_lock();
151 part_stat_inc(part, ios[STAT_FLUSH]);
152 part_stat_add(part, nsecs[STAT_FLUSH],
153 ktime_get_ns() - rq->start_time_ns);
154 part_stat_unlock();
155}
156
157/**
158 * blk_flush_complete_seq - complete flush sequence
159 * @rq: PREFLUSH/FUA request being sequenced
160 * @fq: flush queue
161 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
162 * @error: whether an error occurred
163 *
164 * @rq just completed @seq part of its flush sequence, record the
165 * completion and trigger the next step.
166 *
167 * CONTEXT:
168 * spin_lock_irq(fq->mq_flush_lock)
169 */
170static void blk_flush_complete_seq(struct request *rq,
171 struct blk_flush_queue *fq,
172 unsigned int seq, blk_status_t error)
173{
174 struct request_queue *q = rq->q;
175 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
176 blk_opf_t cmd_flags;
177
178 BUG_ON(rq->flush.seq & seq);
179 rq->flush.seq |= seq;
180 cmd_flags = rq->cmd_flags;
181
182 if (likely(!error))
183 seq = blk_flush_cur_seq(rq);
184 else
185 seq = REQ_FSEQ_DONE;
186
187 switch (seq) {
188 case REQ_FSEQ_PREFLUSH:
189 case REQ_FSEQ_POSTFLUSH:
190 /* queue for flush */
191 if (list_empty(pending))
192 fq->flush_pending_since = jiffies;
193 list_move_tail(&rq->flush.list, pending);
194 break;
195
196 case REQ_FSEQ_DATA:
197 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
198 blk_flush_queue_rq(rq, true);
199 break;
200
201 case REQ_FSEQ_DONE:
202 /*
203 * @rq was previously adjusted by blk_insert_flush() for
204 * flush sequencing and may already have gone through the
205 * flush data request completion path. Restore @rq for
206 * normal completion and end it.
207 */
208 list_del_init(&rq->flush.list);
209 blk_flush_restore_request(rq);
210 blk_mq_end_request(rq, error);
211 break;
212
213 default:
214 BUG();
215 }
216
217 blk_kick_flush(q, fq, cmd_flags);
218}
219
220static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
221 blk_status_t error)
222{
223 struct request_queue *q = flush_rq->q;
224 struct list_head *running;
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 /* release the tag's ownership to the req cloned from */
230 spin_lock_irqsave(&fq->mq_flush_lock, flags);
231
232 if (!req_ref_put_and_test(flush_rq)) {
233 fq->rq_status = error;
234 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
235 return RQ_END_IO_NONE;
236 }
237
238 blk_account_io_flush(flush_rq);
239 /*
240 * Flush request has to be marked as IDLE when it is really ended
241 * because its .end_io() is called from timeout code path too for
242 * avoiding use-after-free.
243 */
244 WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
245 if (fq->rq_status != BLK_STS_OK) {
246 error = fq->rq_status;
247 fq->rq_status = BLK_STS_OK;
248 }
249
250 if (!q->elevator) {
251 flush_rq->tag = BLK_MQ_NO_TAG;
252 } else {
253 blk_mq_put_driver_tag(flush_rq);
254 flush_rq->internal_tag = BLK_MQ_NO_TAG;
255 }
256
257 running = &fq->flush_queue[fq->flush_running_idx];
258 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
259
260 /* account completion of the flush request */
261 fq->flush_running_idx ^= 1;
262
263 /* and push the waiting requests to the next stage */
264 list_for_each_entry_safe(rq, n, running, flush.list) {
265 unsigned int seq = blk_flush_cur_seq(rq);
266
267 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
268 blk_flush_complete_seq(rq, fq, seq, error);
269 }
270
271 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
272 return RQ_END_IO_NONE;
273}
274
275bool is_flush_rq(struct request *rq)
276{
277 return rq->end_io == flush_end_io;
278}
279
280/**
281 * blk_kick_flush - consider issuing flush request
282 * @q: request_queue being kicked
283 * @fq: flush queue
284 * @flags: cmd_flags of the original request
285 *
286 * Flush related states of @q have changed, consider issuing flush request.
287 * Please read the comment at the top of this file for more info.
288 *
289 * CONTEXT:
290 * spin_lock_irq(fq->mq_flush_lock)
291 *
292 */
293static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
294 blk_opf_t flags)
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;
304
305 /* C2 and C3 */
306 if (!list_empty(&fq->flush_data_in_flight) &&
307 time_before(jiffies,
308 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
309 return;
310
311 /*
312 * Issue flush and toggle pending_idx. This makes pending_idx
313 * different from running_idx, which means flush is in flight.
314 */
315 fq->flush_pending_idx ^= 1;
316
317 blk_rq_init(q, flush_rq);
318
319 /*
320 * In case of none scheduler, borrow tag from the first request
321 * since they can't be in flight at the same time. And acquire
322 * the tag's ownership for flush req.
323 *
324 * In case of IO scheduler, flush rq need to borrow scheduler tag
325 * just for cheating put/get driver tag.
326 */
327 flush_rq->mq_ctx = first_rq->mq_ctx;
328 flush_rq->mq_hctx = first_rq->mq_hctx;
329
330 if (!q->elevator) {
331 flush_rq->tag = first_rq->tag;
332
333 /*
334 * We borrow data request's driver tag, so have to mark
335 * this flush request as INFLIGHT for avoiding double
336 * account of this driver tag
337 */
338 flush_rq->rq_flags |= RQF_MQ_INFLIGHT;
339 } else
340 flush_rq->internal_tag = first_rq->internal_tag;
341
342 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
343 flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
344 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
345 flush_rq->end_io = flush_end_io;
346 /*
347 * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
348 * implied in refcount_inc_not_zero() called from
349 * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
350 * and READ flush_rq->end_io
351 */
352 smp_wmb();
353 req_ref_set(flush_rq, 1);
354
355 blk_flush_queue_rq(flush_rq, false);
356}
357
358static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
359 blk_status_t error)
360{
361 struct request_queue *q = rq->q;
362 struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
363 struct blk_mq_ctx *ctx = rq->mq_ctx;
364 unsigned long flags;
365 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
366
367 if (q->elevator) {
368 WARN_ON(rq->tag < 0);
369 blk_mq_put_driver_tag(rq);
370 }
371
372 /*
373 * After populating an empty queue, kick it to avoid stall. Read
374 * the comment in flush_end_io().
375 */
376 spin_lock_irqsave(&fq->mq_flush_lock, flags);
377 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
378 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
379
380 blk_mq_sched_restart(hctx);
381 return RQ_END_IO_NONE;
382}
383
384/**
385 * blk_insert_flush - insert a new PREFLUSH/FUA request
386 * @rq: request to insert
387 *
388 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
389 * or __blk_mq_run_hw_queue() to dispatch request.
390 * @rq is being submitted. Analyze what needs to be done and put it on the
391 * right queue.
392 */
393void blk_insert_flush(struct request *rq)
394{
395 struct request_queue *q = rq->q;
396 unsigned long fflags = q->queue_flags; /* may change, cache */
397 unsigned int policy = blk_flush_policy(fflags, rq);
398 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
399
400 /*
401 * @policy now records what operations need to be done. Adjust
402 * REQ_PREFLUSH and FUA for the driver.
403 */
404 rq->cmd_flags &= ~REQ_PREFLUSH;
405 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
406 rq->cmd_flags &= ~REQ_FUA;
407
408 /*
409 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
410 * of those flags, we have to set REQ_SYNC to avoid skewing
411 * the request accounting.
412 */
413 rq->cmd_flags |= REQ_SYNC;
414
415 /*
416 * An empty flush handed down from a stacking driver may
417 * translate into nothing if the underlying device does not
418 * advertise a write-back cache. In this case, simply
419 * complete the request.
420 */
421 if (!policy) {
422 blk_mq_end_request(rq, 0);
423 return;
424 }
425
426 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
427
428 /*
429 * If there's data but flush is not necessary, the request can be
430 * processed directly without going through flush machinery. Queue
431 * for normal execution.
432 */
433 if ((policy & REQ_FSEQ_DATA) &&
434 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
435 blk_mq_request_bypass_insert(rq, false, true);
436 return;
437 }
438
439 /*
440 * @rq should go through flush machinery. Mark it part of flush
441 * sequence and submit for further processing.
442 */
443 memset(&rq->flush, 0, sizeof(rq->flush));
444 INIT_LIST_HEAD(&rq->flush.list);
445 rq->rq_flags |= RQF_FLUSH_SEQ;
446 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
447
448 rq->end_io = mq_flush_data_end_io;
449
450 spin_lock_irq(&fq->mq_flush_lock);
451 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
452 spin_unlock_irq(&fq->mq_flush_lock);
453}
454
455/**
456 * blkdev_issue_flush - queue a flush
457 * @bdev: blockdev to issue flush for
458 *
459 * Description:
460 * Issue a flush for the block device in question.
461 */
462int blkdev_issue_flush(struct block_device *bdev)
463{
464 struct bio bio;
465
466 bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);
467 return submit_bio_wait(&bio);
468}
469EXPORT_SYMBOL(blkdev_issue_flush);
470
471struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
472 gfp_t flags)
473{
474 struct blk_flush_queue *fq;
475 int rq_sz = sizeof(struct request);
476
477 fq = kzalloc_node(sizeof(*fq), flags, node);
478 if (!fq)
479 goto fail;
480
481 spin_lock_init(&fq->mq_flush_lock);
482
483 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
484 fq->flush_rq = kzalloc_node(rq_sz, flags, node);
485 if (!fq->flush_rq)
486 goto fail_rq;
487
488 INIT_LIST_HEAD(&fq->flush_queue[0]);
489 INIT_LIST_HEAD(&fq->flush_queue[1]);
490 INIT_LIST_HEAD(&fq->flush_data_in_flight);
491
492 return fq;
493
494 fail_rq:
495 kfree(fq);
496 fail:
497 return NULL;
498}
499
500void blk_free_flush_queue(struct blk_flush_queue *fq)
501{
502 /* bio based request queue hasn't flush queue */
503 if (!fq)
504 return;
505
506 kfree(fq->flush_rq);
507 kfree(fq);
508}
509
510/*
511 * Allow driver to set its own lock class to fq->mq_flush_lock for
512 * avoiding lockdep complaint.
513 *
514 * flush_end_io() may be called recursively from some driver, such as
515 * nvme-loop, so lockdep may complain 'possible recursive locking' because
516 * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
517 * key. We need to assign different lock class for these driver's
518 * fq->mq_flush_lock for avoiding the lockdep warning.
519 *
520 * Use dynamically allocated lock class key for each 'blk_flush_queue'
521 * instance is over-kill, and more worse it introduces horrible boot delay
522 * issue because synchronize_rcu() is implied in lockdep_unregister_key which
523 * is called for each hctx release. SCSI probing may synchronously create and
524 * destroy lots of MQ request_queues for non-existent devices, and some robot
525 * test kernel always enable lockdep option. It is observed that more than half
526 * an hour is taken during SCSI MQ probe with per-fq lock class.
527 */
528void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
529 struct lock_class_key *key)
530{
531 lockdep_set_class(&hctx->fq->mq_flush_lock, key);
532}
533EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);
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_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, 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_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 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 RQF_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 long 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 & (1UL << QUEUE_FLAG_WC)) {
106 if (rq->cmd_flags & REQ_PREFLUSH)
107 policy |= REQ_FSEQ_PREFLUSH;
108 if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
109 (rq->cmd_flags & REQ_FUA))
110 policy |= REQ_FSEQ_POSTFLUSH;
111 }
112 return policy;
113}
114
115static unsigned int blk_flush_cur_seq(struct request *rq)
116{
117 return 1 << ffz(rq->flush.seq);
118}
119
120static void blk_flush_restore_request(struct request *rq)
121{
122 /*
123 * After flush data completion, @rq->bio is %NULL but we need to
124 * complete the bio again. @rq->biotail is guaranteed to equal the
125 * original @rq->bio. Restore it.
126 */
127 rq->bio = rq->biotail;
128
129 /* make @rq a normal request */
130 rq->rq_flags &= ~RQF_FLUSH_SEQ;
131 rq->end_io = rq->flush.saved_end_io;
132}
133
134static bool blk_flush_queue_rq(struct request *rq, bool add_front)
135{
136 if (rq->q->mq_ops) {
137 blk_mq_add_to_requeue_list(rq, add_front, true);
138 return false;
139 } else {
140 if (add_front)
141 list_add(&rq->queuelist, &rq->q->queue_head);
142 else
143 list_add_tail(&rq->queuelist, &rq->q->queue_head);
144 return true;
145 }
146}
147
148/**
149 * blk_flush_complete_seq - complete flush sequence
150 * @rq: FLUSH/FUA request being sequenced
151 * @fq: flush queue
152 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
153 * @error: whether an error occurred
154 *
155 * @rq just completed @seq part of its flush sequence, record the
156 * completion and trigger the next step.
157 *
158 * CONTEXT:
159 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
160 *
161 * RETURNS:
162 * %true if requests were added to the dispatch queue, %false otherwise.
163 */
164static bool blk_flush_complete_seq(struct request *rq,
165 struct blk_flush_queue *fq,
166 unsigned int seq, int error)
167{
168 struct request_queue *q = rq->q;
169 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
170 bool queued = false, kicked;
171
172 BUG_ON(rq->flush.seq & seq);
173 rq->flush.seq |= seq;
174
175 if (likely(!error))
176 seq = blk_flush_cur_seq(rq);
177 else
178 seq = REQ_FSEQ_DONE;
179
180 switch (seq) {
181 case REQ_FSEQ_PREFLUSH:
182 case REQ_FSEQ_POSTFLUSH:
183 /* queue for flush */
184 if (list_empty(pending))
185 fq->flush_pending_since = jiffies;
186 list_move_tail(&rq->flush.list, pending);
187 break;
188
189 case REQ_FSEQ_DATA:
190 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
191 queued = blk_flush_queue_rq(rq, true);
192 break;
193
194 case REQ_FSEQ_DONE:
195 /*
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.
200 */
201 BUG_ON(!list_empty(&rq->queuelist));
202 list_del_init(&rq->flush.list);
203 blk_flush_restore_request(rq);
204 if (q->mq_ops)
205 blk_mq_end_request(rq, error);
206 else
207 __blk_end_request_all(rq, error);
208 break;
209
210 default:
211 BUG();
212 }
213
214 kicked = blk_kick_flush(q, fq);
215 return kicked | queued;
216}
217
218static void flush_end_io(struct request *flush_rq, int error)
219{
220 struct request_queue *q = flush_rq->q;
221 struct list_head *running;
222 bool queued = false;
223 struct request *rq, *n;
224 unsigned long flags = 0;
225 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
226
227 if (q->mq_ops) {
228 struct blk_mq_hw_ctx *hctx;
229
230 /* release the tag's ownership to the req cloned from */
231 spin_lock_irqsave(&fq->mq_flush_lock, flags);
232 hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
233 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
234 flush_rq->tag = -1;
235 }
236
237 running = &fq->flush_queue[fq->flush_running_idx];
238 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
239
240 /* account completion of the flush request */
241 fq->flush_running_idx ^= 1;
242
243 if (!q->mq_ops)
244 elv_completed_request(q, flush_rq);
245
246 /* and push the waiting requests to the next stage */
247 list_for_each_entry_safe(rq, n, running, flush.list) {
248 unsigned int seq = blk_flush_cur_seq(rq);
249
250 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
251 queued |= blk_flush_complete_seq(rq, fq, seq, error);
252 }
253
254 /*
255 * Kick the queue to avoid stall for two cases:
256 * 1. Moving a request silently to empty queue_head may stall the
257 * queue.
258 * 2. When flush request is running in non-queueable queue, the
259 * queue is hold. Restart the queue after flush request is finished
260 * to avoid stall.
261 * This function is called from request completion path and calling
262 * directly into request_fn may confuse the driver. Always use
263 * kblockd.
264 */
265 if (queued || fq->flush_queue_delayed) {
266 WARN_ON(q->mq_ops);
267 blk_run_queue_async(q);
268 }
269 fq->flush_queue_delayed = 0;
270 if (q->mq_ops)
271 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
272}
273
274/**
275 * blk_kick_flush - consider issuing flush request
276 * @q: request_queue being kicked
277 * @fq: flush queue
278 *
279 * Flush related states of @q have changed, consider issuing flush request.
280 * Please read the comment at the top of this file for more info.
281 *
282 * CONTEXT:
283 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
284 *
285 * RETURNS:
286 * %true if flush was issued, %false otherwise.
287 */
288static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
289{
290 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
291 struct request *first_rq =
292 list_first_entry(pending, struct request, flush.list);
293 struct request *flush_rq = fq->flush_rq;
294
295 /* C1 described at the top of this file */
296 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
297 return false;
298
299 /* C2 and C3 */
300 if (!list_empty(&fq->flush_data_in_flight) &&
301 time_before(jiffies,
302 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
303 return false;
304
305 /*
306 * Issue flush and toggle pending_idx. This makes pending_idx
307 * different from running_idx, which means flush is in flight.
308 */
309 fq->flush_pending_idx ^= 1;
310
311 blk_rq_init(q, flush_rq);
312
313 /*
314 * Borrow tag from the first request since they can't
315 * be in flight at the same time. And acquire the tag's
316 * ownership for flush req.
317 */
318 if (q->mq_ops) {
319 struct blk_mq_hw_ctx *hctx;
320
321 flush_rq->mq_ctx = first_rq->mq_ctx;
322 flush_rq->tag = first_rq->tag;
323 fq->orig_rq = first_rq;
324
325 hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
326 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
327 }
328
329 flush_rq->cmd_type = REQ_TYPE_FS;
330 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
331 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
332 flush_rq->rq_disk = first_rq->rq_disk;
333 flush_rq->end_io = flush_end_io;
334
335 return blk_flush_queue_rq(flush_rq, false);
336}
337
338static void flush_data_end_io(struct request *rq, int error)
339{
340 struct request_queue *q = rq->q;
341 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
342
343 /*
344 * Updating q->in_flight[] here for making this tag usable
345 * early. Because in blk_queue_start_tag(),
346 * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
347 * reserve tags for sync I/O.
348 *
349 * More importantly this way can avoid the following I/O
350 * deadlock:
351 *
352 * - suppose there are 40 fua requests comming to flush queue
353 * and queue depth is 31
354 * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
355 * tag for async I/O any more
356 * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
357 * and flush_data_end_io() is called
358 * - the other rqs still can't go ahead if not updating
359 * q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
360 * are held in flush data queue and make no progress of
361 * handling post flush rq
362 * - only after the post flush rq is handled, all these rqs
363 * can be completed
364 */
365
366 elv_completed_request(q, rq);
367
368 /* for avoiding double accounting */
369 rq->rq_flags &= ~RQF_STARTED;
370
371 /*
372 * After populating an empty queue, kick it to avoid stall. Read
373 * the comment in flush_end_io().
374 */
375 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
376 blk_run_queue_async(q);
377}
378
379static void mq_flush_data_end_io(struct request *rq, int error)
380{
381 struct request_queue *q = rq->q;
382 struct blk_mq_hw_ctx *hctx;
383 struct blk_mq_ctx *ctx = rq->mq_ctx;
384 unsigned long flags;
385 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
386
387 hctx = blk_mq_map_queue(q, ctx->cpu);
388
389 /*
390 * After populating an empty queue, kick it to avoid stall. Read
391 * the comment in flush_end_io().
392 */
393 spin_lock_irqsave(&fq->mq_flush_lock, flags);
394 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
395 blk_mq_run_hw_queue(hctx, true);
396 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
397}
398
399/**
400 * blk_insert_flush - insert a new FLUSH/FUA request
401 * @rq: request to insert
402 *
403 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
404 * or __blk_mq_run_hw_queue() to dispatch request.
405 * @rq is being submitted. Analyze what needs to be done and put it on the
406 * right queue.
407 *
408 * CONTEXT:
409 * spin_lock_irq(q->queue_lock) in !mq case
410 */
411void blk_insert_flush(struct request *rq)
412{
413 struct request_queue *q = rq->q;
414 unsigned long fflags = q->queue_flags; /* may change, cache */
415 unsigned int policy = blk_flush_policy(fflags, rq);
416 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
417
418 /*
419 * @policy now records what operations need to be done. Adjust
420 * REQ_PREFLUSH and FUA for the driver.
421 */
422 rq->cmd_flags &= ~REQ_PREFLUSH;
423 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
424 rq->cmd_flags &= ~REQ_FUA;
425
426 /*
427 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
428 * of those flags, we have to set REQ_SYNC to avoid skewing
429 * the request accounting.
430 */
431 rq->cmd_flags |= REQ_SYNC;
432
433 /*
434 * An empty flush handed down from a stacking driver may
435 * translate into nothing if the underlying device does not
436 * advertise a write-back cache. In this case, simply
437 * complete the request.
438 */
439 if (!policy) {
440 if (q->mq_ops)
441 blk_mq_end_request(rq, 0);
442 else
443 __blk_end_bidi_request(rq, 0, 0, 0);
444 return;
445 }
446
447 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
448
449 /*
450 * If there's data but flush is not necessary, the request can be
451 * processed directly without going through flush machinery. Queue
452 * for normal execution.
453 */
454 if ((policy & REQ_FSEQ_DATA) &&
455 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
456 if (q->mq_ops) {
457 blk_mq_insert_request(rq, false, true, false);
458 } else
459 list_add_tail(&rq->queuelist, &q->queue_head);
460 return;
461 }
462
463 /*
464 * @rq should go through flush machinery. Mark it part of flush
465 * sequence and submit for further processing.
466 */
467 memset(&rq->flush, 0, sizeof(rq->flush));
468 INIT_LIST_HEAD(&rq->flush.list);
469 rq->rq_flags |= RQF_FLUSH_SEQ;
470 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
471 if (q->mq_ops) {
472 rq->end_io = mq_flush_data_end_io;
473
474 spin_lock_irq(&fq->mq_flush_lock);
475 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
476 spin_unlock_irq(&fq->mq_flush_lock);
477 return;
478 }
479 rq->end_io = flush_data_end_io;
480
481 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
482}
483
484/**
485 * blkdev_issue_flush - queue a flush
486 * @bdev: blockdev to issue flush for
487 * @gfp_mask: memory allocation flags (for bio_alloc)
488 * @error_sector: error sector
489 *
490 * Description:
491 * Issue a flush for the block device in question. Caller can supply
492 * room for storing the error offset in case of a flush error, if they
493 * wish to. If WAIT flag is not passed then caller may check only what
494 * request was pushed in some internal queue for later handling.
495 */
496int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
497 sector_t *error_sector)
498{
499 struct request_queue *q;
500 struct bio *bio;
501 int ret = 0;
502
503 if (bdev->bd_disk == NULL)
504 return -ENXIO;
505
506 q = bdev_get_queue(bdev);
507 if (!q)
508 return -ENXIO;
509
510 /*
511 * some block devices may not have their queue correctly set up here
512 * (e.g. loop device without a backing file) and so issuing a flush
513 * here will panic. Ensure there is a request function before issuing
514 * the flush.
515 */
516 if (!q->make_request_fn)
517 return -ENXIO;
518
519 bio = bio_alloc(gfp_mask, 0);
520 bio->bi_bdev = bdev;
521 bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
522
523 ret = submit_bio_wait(bio);
524
525 /*
526 * The driver must store the error location in ->bi_sector, if
527 * it supports it. For non-stacked drivers, this should be
528 * copied from blk_rq_pos(rq).
529 */
530 if (error_sector)
531 *error_sector = bio->bi_iter.bi_sector;
532
533 bio_put(bio);
534 return ret;
535}
536EXPORT_SYMBOL(blkdev_issue_flush);
537
538struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
539 int node, int cmd_size)
540{
541 struct blk_flush_queue *fq;
542 int rq_sz = sizeof(struct request);
543
544 fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
545 if (!fq)
546 goto fail;
547
548 if (q->mq_ops) {
549 spin_lock_init(&fq->mq_flush_lock);
550 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
551 }
552
553 fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
554 if (!fq->flush_rq)
555 goto fail_rq;
556
557 INIT_LIST_HEAD(&fq->flush_queue[0]);
558 INIT_LIST_HEAD(&fq->flush_queue[1]);
559 INIT_LIST_HEAD(&fq->flush_data_in_flight);
560
561 return fq;
562
563 fail_rq:
564 kfree(fq);
565 fail:
566 return NULL;
567}
568
569void blk_free_flush_queue(struct blk_flush_queue *fq)
570{
571 /* bio based request queue hasn't flush queue */
572 if (!fq)
573 return;
574
575 kfree(fq->flush_rq);
576 kfree(fq);
577}