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
73 #include "blk.h"
74 #include "blk-mq.h"
75 #include "blk-mq-tag.h"
76 #include "blk-mq-sched.h"
77
78 /* PREFLUSH/FUA sequences */
79 enum {
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
95 static void blk_kick_flush(struct request_queue *q,
96 struct blk_flush_queue *fq, unsigned int flags);
97
blk_flush_policy(unsigned long fflags,struct request * rq)98 static 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
blk_flush_cur_seq(struct request * rq)115 static unsigned int blk_flush_cur_seq(struct request *rq)
116 {
117 return 1 << ffz(rq->flush.seq);
118 }
119
blk_flush_restore_request(struct request * rq)120 static 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
blk_flush_queue_rq(struct request * rq,bool add_front)134 static void blk_flush_queue_rq(struct request *rq, bool add_front)
135 {
136 blk_mq_add_to_requeue_list(rq, add_front, true);
137 }
138
blk_account_io_flush(struct request * rq)139 static void blk_account_io_flush(struct request *rq)
140 {
141 struct block_device *part = rq->rq_disk->part0;
142
143 part_stat_lock();
144 part_stat_inc(part, ios[STAT_FLUSH]);
145 part_stat_add(part, nsecs[STAT_FLUSH],
146 ktime_get_ns() - rq->start_time_ns);
147 part_stat_unlock();
148 }
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 */
blk_flush_complete_seq(struct request * rq,struct blk_flush_queue * fq,unsigned int seq,blk_status_t error)163 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 struct request_queue *q = rq->q;
168 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
169 unsigned int cmd_flags;
170
171 BUG_ON(rq->flush.seq & seq);
172 rq->flush.seq |= seq;
173 cmd_flags = rq->cmd_flags;
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 blk_flush_queue_rq(rq, true);
192 break;
193
194 case REQ_FSEQ_DONE:
195 /*
196 * @rq was previously adjusted by blk_insert_flush() 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 blk_mq_end_request(rq, error);
205 break;
206
207 default:
208 BUG();
209 }
210
211 blk_kick_flush(q, fq, cmd_flags);
212 }
213
flush_end_io(struct request * flush_rq,blk_status_t error)214 static void flush_end_io(struct request *flush_rq, blk_status_t error)
215 {
216 struct request_queue *q = flush_rq->q;
217 struct list_head *running;
218 struct request *rq, *n;
219 unsigned long flags = 0;
220 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
221
222 /* release the tag's ownership to the req cloned from */
223 spin_lock_irqsave(&fq->mq_flush_lock, flags);
224
225 if (!refcount_dec_and_test(&flush_rq->ref)) {
226 fq->rq_status = error;
227 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
228 return;
229 }
230
231 blk_account_io_flush(flush_rq);
232 /*
233 * Flush request has to be marked as IDLE when it is really ended
234 * because its .end_io() is called from timeout code path too for
235 * avoiding use-after-free.
236 */
237 WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
238 if (fq->rq_status != BLK_STS_OK)
239 error = fq->rq_status;
240
241 if (!q->elevator) {
242 flush_rq->tag = BLK_MQ_NO_TAG;
243 } else {
244 blk_mq_put_driver_tag(flush_rq);
245 flush_rq->internal_tag = BLK_MQ_NO_TAG;
246 }
247
248 running = &fq->flush_queue[fq->flush_running_idx];
249 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
250
251 /* account completion of the flush request */
252 fq->flush_running_idx ^= 1;
253
254 /* and push the waiting requests to the next stage */
255 list_for_each_entry_safe(rq, n, running, flush.list) {
256 unsigned int seq = blk_flush_cur_seq(rq);
257
258 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
259 blk_flush_complete_seq(rq, fq, seq, error);
260 }
261
262 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
263 }
264
is_flush_rq(struct request * rq)265 bool is_flush_rq(struct request *rq)
266 {
267 return rq->end_io == flush_end_io;
268 }
269
270 /**
271 * blk_kick_flush - consider issuing flush request
272 * @q: request_queue being kicked
273 * @fq: flush queue
274 * @flags: cmd_flags of the original request
275 *
276 * Flush related states of @q have changed, consider issuing flush request.
277 * Please read the comment at the top of this file for more info.
278 *
279 * CONTEXT:
280 * spin_lock_irq(fq->mq_flush_lock)
281 *
282 */
blk_kick_flush(struct request_queue * q,struct blk_flush_queue * fq,unsigned int flags)283 static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
284 unsigned int flags)
285 {
286 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
287 struct request *first_rq =
288 list_first_entry(pending, struct request, flush.list);
289 struct request *flush_rq = fq->flush_rq;
290
291 /* C1 described at the top of this file */
292 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
293 return;
294
295 /* C2 and C3 */
296 if (!list_empty(&fq->flush_data_in_flight) &&
297 time_before(jiffies,
298 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
299 return;
300
301 /*
302 * Issue flush and toggle pending_idx. This makes pending_idx
303 * different from running_idx, which means flush is in flight.
304 */
305 fq->flush_pending_idx ^= 1;
306
307 blk_rq_init(q, flush_rq);
308
309 /*
310 * In case of none scheduler, borrow tag from the first request
311 * since they can't be in flight at the same time. And acquire
312 * the tag's ownership for flush req.
313 *
314 * In case of IO scheduler, flush rq need to borrow scheduler tag
315 * just for cheating put/get driver tag.
316 */
317 flush_rq->mq_ctx = first_rq->mq_ctx;
318 flush_rq->mq_hctx = first_rq->mq_hctx;
319
320 if (!q->elevator) {
321 flush_rq->tag = first_rq->tag;
322
323 /*
324 * We borrow data request's driver tag, so have to mark
325 * this flush request as INFLIGHT for avoiding double
326 * account of this driver tag
327 */
328 flush_rq->rq_flags |= RQF_MQ_INFLIGHT;
329 } else
330 flush_rq->internal_tag = first_rq->internal_tag;
331
332 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
333 flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
334 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
335 flush_rq->rq_disk = first_rq->rq_disk;
336 flush_rq->end_io = flush_end_io;
337 /*
338 * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
339 * implied in refcount_inc_not_zero() called from
340 * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
341 * and READ flush_rq->end_io
342 */
343 smp_wmb();
344 refcount_set(&flush_rq->ref, 1);
345
346 blk_flush_queue_rq(flush_rq, false);
347 }
348
mq_flush_data_end_io(struct request * rq,blk_status_t error)349 static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
350 {
351 struct request_queue *q = rq->q;
352 struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
353 struct blk_mq_ctx *ctx = rq->mq_ctx;
354 unsigned long flags;
355 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
356
357 if (q->elevator) {
358 WARN_ON(rq->tag < 0);
359 blk_mq_put_driver_tag(rq);
360 }
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 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
368 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
369
370 blk_mq_sched_restart(hctx);
371 }
372
373 /**
374 * blk_insert_flush - insert a new PREFLUSH/FUA request
375 * @rq: request to insert
376 *
377 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
378 * or __blk_mq_run_hw_queue() to dispatch request.
379 * @rq is being submitted. Analyze what needs to be done and put it on the
380 * right queue.
381 */
blk_insert_flush(struct request * rq)382 void blk_insert_flush(struct request *rq)
383 {
384 struct request_queue *q = rq->q;
385 unsigned long fflags = q->queue_flags; /* may change, cache */
386 unsigned int policy = blk_flush_policy(fflags, rq);
387 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
388
389 /*
390 * @policy now records what operations need to be done. Adjust
391 * REQ_PREFLUSH and FUA for the driver.
392 */
393 rq->cmd_flags &= ~REQ_PREFLUSH;
394 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
395 rq->cmd_flags &= ~REQ_FUA;
396
397 /*
398 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
399 * of those flags, we have to set REQ_SYNC to avoid skewing
400 * the request accounting.
401 */
402 rq->cmd_flags |= REQ_SYNC;
403
404 /*
405 * An empty flush handed down from a stacking driver may
406 * translate into nothing if the underlying device does not
407 * advertise a write-back cache. In this case, simply
408 * complete the request.
409 */
410 if (!policy) {
411 blk_mq_end_request(rq, 0);
412 return;
413 }
414
415 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
416
417 /*
418 * If there's data but flush is not necessary, the request can be
419 * processed directly without going through flush machinery. Queue
420 * for normal execution.
421 */
422 if ((policy & REQ_FSEQ_DATA) &&
423 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
424 blk_mq_request_bypass_insert(rq, false, false);
425 return;
426 }
427
428 /*
429 * @rq should go through flush machinery. Mark it part of flush
430 * sequence and submit for further processing.
431 */
432 memset(&rq->flush, 0, sizeof(rq->flush));
433 INIT_LIST_HEAD(&rq->flush.list);
434 rq->rq_flags |= RQF_FLUSH_SEQ;
435 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
436
437 rq->end_io = mq_flush_data_end_io;
438
439 spin_lock_irq(&fq->mq_flush_lock);
440 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
441 spin_unlock_irq(&fq->mq_flush_lock);
442 }
443
444 /**
445 * blkdev_issue_flush - queue a flush
446 * @bdev: blockdev to issue flush for
447 *
448 * Description:
449 * Issue a flush for the block device in question.
450 */
blkdev_issue_flush(struct block_device * bdev)451 int blkdev_issue_flush(struct block_device *bdev)
452 {
453 struct bio bio;
454
455 bio_init(&bio, NULL, 0);
456 bio_set_dev(&bio, bdev);
457 bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
458 return submit_bio_wait(&bio);
459 }
460 EXPORT_SYMBOL(blkdev_issue_flush);
461
blk_alloc_flush_queue(int node,int cmd_size,gfp_t flags)462 struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
463 gfp_t flags)
464 {
465 struct blk_flush_queue *fq;
466 int rq_sz = sizeof(struct request);
467
468 fq = kzalloc_node(sizeof(*fq), flags, node);
469 if (!fq)
470 goto fail;
471
472 spin_lock_init(&fq->mq_flush_lock);
473
474 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
475 fq->flush_rq = kzalloc_node(rq_sz, flags, node);
476 if (!fq->flush_rq)
477 goto fail_rq;
478
479 INIT_LIST_HEAD(&fq->flush_queue[0]);
480 INIT_LIST_HEAD(&fq->flush_queue[1]);
481 INIT_LIST_HEAD(&fq->flush_data_in_flight);
482
483 return fq;
484
485 fail_rq:
486 kfree(fq);
487 fail:
488 return NULL;
489 }
490
blk_free_flush_queue(struct blk_flush_queue * fq)491 void blk_free_flush_queue(struct blk_flush_queue *fq)
492 {
493 /* bio based request queue hasn't flush queue */
494 if (!fq)
495 return;
496
497 kfree(fq->flush_rq);
498 kfree(fq);
499 }
500
501 /*
502 * Allow driver to set its own lock class to fq->mq_flush_lock for
503 * avoiding lockdep complaint.
504 *
505 * flush_end_io() may be called recursively from some driver, such as
506 * nvme-loop, so lockdep may complain 'possible recursive locking' because
507 * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
508 * key. We need to assign different lock class for these driver's
509 * fq->mq_flush_lock for avoiding the lockdep warning.
510 *
511 * Use dynamically allocated lock class key for each 'blk_flush_queue'
512 * instance is over-kill, and more worse it introduces horrible boot delay
513 * issue because synchronize_rcu() is implied in lockdep_unregister_key which
514 * is called for each hctx release. SCSI probing may synchronously create and
515 * destroy lots of MQ request_queues for non-existent devices, and some robot
516 * test kernel always enable lockdep option. It is observed that more than half
517 * an hour is taken during SCSI MQ probe with per-fq lock class.
518 */
blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx * hctx,struct lock_class_key * key)519 void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
520 struct lock_class_key *key)
521 {
522 lockdep_set_class(&hctx->fq->mq_flush_lock, key);
523 }
524 EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);
525
