Line data Source code
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/part_stat.h>
72 :
73 : #include "blk.h"
74 : #include "blk-mq.h"
75 : #include "blk-mq-sched.h"
76 :
77 : /* PREFLUSH/FUA sequences */
78 : enum {
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),
83 :
84 : REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
85 : REQ_FSEQ_POSTFLUSH,
86 :
87 : /*
88 : * If flush has been pending longer than the following timeout,
89 : * it's issued even if flush_data requests are still in flight.
90 : */
91 : FLUSH_PENDING_TIMEOUT = 5 * HZ,
92 : };
93 :
94 : static void blk_kick_flush(struct request_queue *q,
95 : struct blk_flush_queue *fq, blk_opf_t flags);
96 :
97 : static inline struct blk_flush_queue *
98 : blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
99 : {
100 0 : return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
101 : }
102 :
103 : static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
104 : {
105 0 : unsigned int policy = 0;
106 :
107 0 : if (blk_rq_sectors(rq))
108 0 : policy |= REQ_FSEQ_DATA;
109 :
110 0 : if (fflags & (1UL << QUEUE_FLAG_WC)) {
111 0 : if (rq->cmd_flags & REQ_PREFLUSH)
112 0 : policy |= REQ_FSEQ_PREFLUSH;
113 0 : if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
114 0 : (rq->cmd_flags & REQ_FUA))
115 0 : policy |= REQ_FSEQ_POSTFLUSH;
116 : }
117 : return policy;
118 : }
119 :
120 : static unsigned int blk_flush_cur_seq(struct request *rq)
121 : {
122 0 : return 1 << ffz(rq->flush.seq);
123 : }
124 :
125 : static void blk_flush_restore_request(struct request *rq)
126 : {
127 : /*
128 : * After flush data completion, @rq->bio is %NULL but we need to
129 : * complete the bio again. @rq->biotail is guaranteed to equal the
130 : * original @rq->bio. Restore it.
131 : */
132 0 : rq->bio = rq->biotail;
133 :
134 : /* make @rq a normal request */
135 0 : rq->rq_flags &= ~RQF_FLUSH_SEQ;
136 0 : rq->end_io = rq->flush.saved_end_io;
137 : }
138 :
139 0 : static void blk_account_io_flush(struct request *rq)
140 : {
141 0 : struct block_device *part = rq->q->disk->part0;
142 :
143 0 : part_stat_lock();
144 0 : part_stat_inc(part, ios[STAT_FLUSH]);
145 0 : part_stat_add(part, nsecs[STAT_FLUSH],
146 : ktime_get_ns() - rq->start_time_ns);
147 0 : part_stat_unlock();
148 0 : }
149 :
150 : /**
151 : * blk_flush_complete_seq - complete flush sequence
152 : * @rq: PREFLUSH/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(fq->mq_flush_lock)
162 : */
163 0 : static void blk_flush_complete_seq(struct request *rq,
164 : struct blk_flush_queue *fq,
165 : unsigned int seq, blk_status_t error)
166 : {
167 0 : struct request_queue *q = rq->q;
168 0 : struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
169 : blk_opf_t cmd_flags;
170 :
171 0 : BUG_ON(rq->flush.seq & seq);
172 0 : rq->flush.seq |= seq;
173 0 : cmd_flags = rq->cmd_flags;
174 :
175 0 : if (likely(!error))
176 0 : seq = blk_flush_cur_seq(rq);
177 : else
178 : seq = REQ_FSEQ_DONE;
179 :
180 0 : switch (seq) {
181 : case REQ_FSEQ_PREFLUSH:
182 : case REQ_FSEQ_POSTFLUSH:
183 : /* queue for flush */
184 0 : if (list_empty(pending))
185 0 : fq->flush_pending_since = jiffies;
186 0 : list_move_tail(&rq->flush.list, pending);
187 : break;
188 :
189 : case REQ_FSEQ_DATA:
190 0 : list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
191 0 : spin_lock(&q->requeue_lock);
192 0 : list_add(&rq->queuelist, &q->requeue_list);
193 0 : spin_unlock(&q->requeue_lock);
194 0 : blk_mq_kick_requeue_list(q);
195 0 : break;
196 :
197 : case REQ_FSEQ_DONE:
198 : /*
199 : * @rq was previously adjusted by blk_insert_flush() for
200 : * flush sequencing and may already have gone through the
201 : * flush data request completion path. Restore @rq for
202 : * normal completion and end it.
203 : */
204 0 : list_del_init(&rq->flush.list);
205 0 : blk_flush_restore_request(rq);
206 0 : blk_mq_end_request(rq, error);
207 0 : break;
208 :
209 : default:
210 0 : BUG();
211 : }
212 :
213 0 : blk_kick_flush(q, fq, cmd_flags);
214 0 : }
215 :
216 0 : static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
217 : blk_status_t error)
218 : {
219 0 : struct request_queue *q = flush_rq->q;
220 : struct list_head *running;
221 : struct request *rq, *n;
222 0 : unsigned long flags = 0;
223 0 : struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
224 :
225 : /* release the tag's ownership to the req cloned from */
226 0 : spin_lock_irqsave(&fq->mq_flush_lock, flags);
227 :
228 0 : if (!req_ref_put_and_test(flush_rq)) {
229 0 : fq->rq_status = error;
230 0 : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
231 0 : return RQ_END_IO_NONE;
232 : }
233 :
234 0 : blk_account_io_flush(flush_rq);
235 : /*
236 : * Flush request has to be marked as IDLE when it is really ended
237 : * because its .end_io() is called from timeout code path too for
238 : * avoiding use-after-free.
239 : */
240 0 : WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
241 0 : if (fq->rq_status != BLK_STS_OK) {
242 0 : error = fq->rq_status;
243 0 : fq->rq_status = BLK_STS_OK;
244 : }
245 :
246 0 : if (!q->elevator) {
247 0 : flush_rq->tag = BLK_MQ_NO_TAG;
248 : } else {
249 0 : blk_mq_put_driver_tag(flush_rq);
250 0 : flush_rq->internal_tag = BLK_MQ_NO_TAG;
251 : }
252 :
253 0 : running = &fq->flush_queue[fq->flush_running_idx];
254 0 : BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
255 :
256 : /* account completion of the flush request */
257 0 : fq->flush_running_idx ^= 1;
258 :
259 : /* and push the waiting requests to the next stage */
260 0 : list_for_each_entry_safe(rq, n, running, flush.list) {
261 0 : unsigned int seq = blk_flush_cur_seq(rq);
262 :
263 0 : BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
264 0 : blk_flush_complete_seq(rq, fq, seq, error);
265 : }
266 :
267 0 : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
268 0 : return RQ_END_IO_NONE;
269 : }
270 :
271 0 : bool is_flush_rq(struct request *rq)
272 : {
273 0 : return rq->end_io == flush_end_io;
274 : }
275 :
276 : /**
277 : * blk_kick_flush - consider issuing flush request
278 : * @q: request_queue being kicked
279 : * @fq: flush queue
280 : * @flags: cmd_flags of the original request
281 : *
282 : * Flush related states of @q have changed, consider issuing flush request.
283 : * Please read the comment at the top of this file for more info.
284 : *
285 : * CONTEXT:
286 : * spin_lock_irq(fq->mq_flush_lock)
287 : *
288 : */
289 0 : static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
290 : blk_opf_t flags)
291 : {
292 0 : struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
293 0 : struct request *first_rq =
294 0 : list_first_entry(pending, struct request, flush.list);
295 0 : struct request *flush_rq = fq->flush_rq;
296 :
297 : /* C1 described at the top of this file */
298 0 : if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
299 : return;
300 :
301 : /* C2 and C3 */
302 0 : if (!list_empty(&fq->flush_data_in_flight) &&
303 0 : time_before(jiffies,
304 : fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
305 : return;
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 0 : fq->flush_pending_idx ^= 1;
312 :
313 0 : blk_rq_init(q, flush_rq);
314 :
315 : /*
316 : * In case of none scheduler, borrow tag from the first request
317 : * since they can't be in flight at the same time. And acquire
318 : * the tag's ownership for flush req.
319 : *
320 : * In case of IO scheduler, flush rq need to borrow scheduler tag
321 : * just for cheating put/get driver tag.
322 : */
323 0 : flush_rq->mq_ctx = first_rq->mq_ctx;
324 0 : flush_rq->mq_hctx = first_rq->mq_hctx;
325 :
326 0 : if (!q->elevator) {
327 0 : flush_rq->tag = first_rq->tag;
328 :
329 : /*
330 : * We borrow data request's driver tag, so have to mark
331 : * this flush request as INFLIGHT for avoiding double
332 : * account of this driver tag
333 : */
334 0 : flush_rq->rq_flags |= RQF_MQ_INFLIGHT;
335 : } else
336 0 : flush_rq->internal_tag = first_rq->internal_tag;
337 :
338 : flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
339 0 : flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
340 0 : flush_rq->rq_flags |= RQF_FLUSH_SEQ;
341 0 : flush_rq->end_io = flush_end_io;
342 : /*
343 : * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
344 : * implied in refcount_inc_not_zero() called from
345 : * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
346 : * and READ flush_rq->end_io
347 : */
348 0 : smp_wmb();
349 0 : req_ref_set(flush_rq, 1);
350 :
351 0 : spin_lock(&q->requeue_lock);
352 0 : list_add_tail(&flush_rq->queuelist, &q->flush_list);
353 0 : spin_unlock(&q->requeue_lock);
354 :
355 0 : blk_mq_kick_requeue_list(q);
356 : }
357 :
358 0 : static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
359 : blk_status_t error)
360 : {
361 0 : struct request_queue *q = rq->q;
362 0 : struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
363 0 : struct blk_mq_ctx *ctx = rq->mq_ctx;
364 : unsigned long flags;
365 0 : struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
366 :
367 0 : if (q->elevator) {
368 0 : 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 0 : spin_lock_irqsave(&fq->mq_flush_lock, flags);
377 0 : blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
378 0 : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
379 :
380 0 : blk_mq_sched_restart(hctx);
381 0 : return RQ_END_IO_NONE;
382 : }
383 :
384 : static void blk_rq_init_flush(struct request *rq)
385 : {
386 0 : rq->flush.seq = 0;
387 0 : INIT_LIST_HEAD(&rq->flush.list);
388 0 : rq->rq_flags |= RQF_FLUSH_SEQ;
389 0 : rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
390 0 : rq->end_io = mq_flush_data_end_io;
391 : }
392 :
393 : /*
394 : * Insert a PREFLUSH/FUA request into the flush state machine.
395 : * Returns true if the request has been consumed by the flush state machine,
396 : * or false if the caller should continue to process it.
397 : */
398 0 : bool blk_insert_flush(struct request *rq)
399 : {
400 0 : struct request_queue *q = rq->q;
401 0 : unsigned long fflags = q->queue_flags; /* may change, cache */
402 0 : unsigned int policy = blk_flush_policy(fflags, rq);
403 0 : struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
404 :
405 : /* FLUSH/FUA request must never be merged */
406 0 : WARN_ON_ONCE(rq->bio != rq->biotail);
407 :
408 : /*
409 : * @policy now records what operations need to be done. Adjust
410 : * REQ_PREFLUSH and FUA for the driver.
411 : */
412 0 : rq->cmd_flags &= ~REQ_PREFLUSH;
413 0 : if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
414 0 : rq->cmd_flags &= ~REQ_FUA;
415 :
416 : /*
417 : * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
418 : * of those flags, we have to set REQ_SYNC to avoid skewing
419 : * the request accounting.
420 : */
421 0 : rq->cmd_flags |= REQ_SYNC;
422 :
423 0 : switch (policy) {
424 : case 0:
425 : /*
426 : * An empty flush handed down from a stacking driver may
427 : * translate into nothing if the underlying device does not
428 : * advertise a write-back cache. In this case, simply
429 : * complete the request.
430 : */
431 0 : blk_mq_end_request(rq, 0);
432 0 : return true;
433 : case REQ_FSEQ_DATA:
434 : /*
435 : * If there's data, but no flush is necessary, the request can
436 : * be processed directly without going through flush machinery.
437 : * Queue for normal execution.
438 : */
439 : return false;
440 : case REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH:
441 : /*
442 : * Initialize the flush fields and completion handler to trigger
443 : * the post flush, and then just pass the command on.
444 : */
445 0 : blk_rq_init_flush(rq);
446 0 : rq->flush.seq |= REQ_FSEQ_POSTFLUSH;
447 0 : spin_lock_irq(&fq->mq_flush_lock);
448 0 : list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
449 0 : spin_unlock_irq(&fq->mq_flush_lock);
450 0 : return false;
451 : default:
452 : /*
453 : * Mark the request as part of a flush sequence and submit it
454 : * for further processing to the flush state machine.
455 : */
456 0 : blk_rq_init_flush(rq);
457 0 : spin_lock_irq(&fq->mq_flush_lock);
458 0 : blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
459 0 : spin_unlock_irq(&fq->mq_flush_lock);
460 0 : return true;
461 : }
462 : }
463 :
464 : /**
465 : * blkdev_issue_flush - queue a flush
466 : * @bdev: blockdev to issue flush for
467 : *
468 : * Description:
469 : * Issue a flush for the block device in question.
470 : */
471 0 : int blkdev_issue_flush(struct block_device *bdev)
472 : {
473 : struct bio bio;
474 :
475 0 : bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);
476 0 : return submit_bio_wait(&bio);
477 : }
478 : EXPORT_SYMBOL(blkdev_issue_flush);
479 :
480 0 : struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
481 : gfp_t flags)
482 : {
483 : struct blk_flush_queue *fq;
484 0 : int rq_sz = sizeof(struct request);
485 :
486 0 : fq = kzalloc_node(sizeof(*fq), flags, node);
487 0 : if (!fq)
488 : goto fail;
489 :
490 0 : spin_lock_init(&fq->mq_flush_lock);
491 :
492 0 : rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
493 0 : fq->flush_rq = kzalloc_node(rq_sz, flags, node);
494 0 : if (!fq->flush_rq)
495 : goto fail_rq;
496 :
497 0 : INIT_LIST_HEAD(&fq->flush_queue[0]);
498 0 : INIT_LIST_HEAD(&fq->flush_queue[1]);
499 0 : INIT_LIST_HEAD(&fq->flush_data_in_flight);
500 :
501 0 : return fq;
502 :
503 : fail_rq:
504 0 : kfree(fq);
505 : fail:
506 : return NULL;
507 : }
508 :
509 0 : void blk_free_flush_queue(struct blk_flush_queue *fq)
510 : {
511 : /* bio based request queue hasn't flush queue */
512 0 : if (!fq)
513 : return;
514 :
515 0 : kfree(fq->flush_rq);
516 0 : kfree(fq);
517 : }
518 :
519 : /*
520 : * Allow driver to set its own lock class to fq->mq_flush_lock for
521 : * avoiding lockdep complaint.
522 : *
523 : * flush_end_io() may be called recursively from some driver, such as
524 : * nvme-loop, so lockdep may complain 'possible recursive locking' because
525 : * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
526 : * key. We need to assign different lock class for these driver's
527 : * fq->mq_flush_lock for avoiding the lockdep warning.
528 : *
529 : * Use dynamically allocated lock class key for each 'blk_flush_queue'
530 : * instance is over-kill, and more worse it introduces horrible boot delay
531 : * issue because synchronize_rcu() is implied in lockdep_unregister_key which
532 : * is called for each hctx release. SCSI probing may synchronously create and
533 : * destroy lots of MQ request_queues for non-existent devices, and some robot
534 : * test kernel always enable lockdep option. It is observed that more than half
535 : * an hour is taken during SCSI MQ probe with per-fq lock class.
536 : */
537 0 : void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
538 : struct lock_class_key *key)
539 : {
540 : lockdep_set_class(&hctx->fq->mq_flush_lock, key);
541 0 : }
542 : EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);
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