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
139 /**
140 * blk_flush_complete_seq - complete flush sequence
141 * @rq: PREFLUSH/FUA request being sequenced
142 * @fq: flush queue
143 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
144 * @error: whether an error occurred
145 *
146 * @rq just completed @seq part of its flush sequence, record the
147 * completion and trigger the next step.
148 *
149 * CONTEXT:
150 * spin_lock_irq(fq->mq_flush_lock)
151 *
152 * RETURNS:
153 * %true if requests were added to the dispatch queue, %false otherwise.
154 */
blk_flush_complete_seq(struct request * rq,struct blk_flush_queue * fq,unsigned int seq,blk_status_t error)155 static void blk_flush_complete_seq(struct request *rq,
156 struct blk_flush_queue *fq,
157 unsigned int seq, blk_status_t error)
158 {
159 struct request_queue *q = rq->q;
160 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
161 unsigned int cmd_flags;
162
163 BUG_ON(rq->flush.seq & seq);
164 rq->flush.seq |= seq;
165 cmd_flags = rq->cmd_flags;
166
167 if (likely(!error))
168 seq = blk_flush_cur_seq(rq);
169 else
170 seq = REQ_FSEQ_DONE;
171
172 switch (seq) {
173 case REQ_FSEQ_PREFLUSH:
174 case REQ_FSEQ_POSTFLUSH:
175 /* queue for flush */
176 if (list_empty(pending))
177 fq->flush_pending_since = jiffies;
178 list_move_tail(&rq->flush.list, pending);
179 break;
180
181 case REQ_FSEQ_DATA:
182 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
183 blk_flush_queue_rq(rq, true);
184 break;
185
186 case REQ_FSEQ_DONE:
187 /*
188 * @rq was previously adjusted by blk_flush_issue() for
189 * flush sequencing and may already have gone through the
190 * flush data request completion path. Restore @rq for
191 * normal completion and end it.
192 */
193 BUG_ON(!list_empty(&rq->queuelist));
194 list_del_init(&rq->flush.list);
195 blk_flush_restore_request(rq);
196 blk_mq_end_request(rq, error);
197 break;
198
199 default:
200 BUG();
201 }
202
203 blk_kick_flush(q, fq, cmd_flags);
204 }
205
flush_end_io(struct request * flush_rq,blk_status_t error)206 static void flush_end_io(struct request *flush_rq, blk_status_t error)
207 {
208 struct request_queue *q = flush_rq->q;
209 struct list_head *running;
210 struct request *rq, *n;
211 unsigned long flags = 0;
212 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
213 struct blk_mq_hw_ctx *hctx;
214
215 /* release the tag's ownership to the req cloned from */
216 spin_lock_irqsave(&fq->mq_flush_lock, flags);
217
218 if (!refcount_dec_and_test(&flush_rq->ref)) {
219 fq->rq_status = error;
220 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
221 return;
222 }
223
224 if (fq->rq_status != BLK_STS_OK)
225 error = fq->rq_status;
226
227 hctx = flush_rq->mq_hctx;
228 if (!q->elevator) {
229 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
230 flush_rq->tag = -1;
231 } else {
232 blk_mq_put_driver_tag(flush_rq);
233 flush_rq->internal_tag = -1;
234 }
235
236 running = &fq->flush_queue[fq->flush_running_idx];
237 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
238
239 /* account completion of the flush request */
240 fq->flush_running_idx ^= 1;
241
242 /* and push the waiting requests to the next stage */
243 list_for_each_entry_safe(rq, n, running, flush.list) {
244 unsigned int seq = blk_flush_cur_seq(rq);
245
246 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
247 blk_flush_complete_seq(rq, fq, seq, error);
248 }
249
250 fq->flush_queue_delayed = 0;
251 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
252 }
253
254 /**
255 * blk_kick_flush - consider issuing flush request
256 * @q: request_queue being kicked
257 * @fq: flush queue
258 * @flags: cmd_flags of the original request
259 *
260 * Flush related states of @q have changed, consider issuing flush request.
261 * Please read the comment at the top of this file for more info.
262 *
263 * CONTEXT:
264 * spin_lock_irq(fq->mq_flush_lock)
265 *
266 */
blk_kick_flush(struct request_queue * q,struct blk_flush_queue * fq,unsigned int flags)267 static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
268 unsigned int flags)
269 {
270 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
271 struct request *first_rq =
272 list_first_entry(pending, struct request, flush.list);
273 struct request *flush_rq = fq->flush_rq;
274
275 /* C1 described at the top of this file */
276 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
277 return;
278
279 /* C2 and C3
280 *
281 * For blk-mq + scheduling, we can risk having all driver tags
282 * assigned to empty flushes, and we deadlock if we are expecting
283 * other requests to make progress. Don't defer for that case.
284 */
285 if (!list_empty(&fq->flush_data_in_flight) && q->elevator &&
286 time_before(jiffies,
287 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
288 return;
289
290 /*
291 * Issue flush and toggle pending_idx. This makes pending_idx
292 * different from running_idx, which means flush is in flight.
293 */
294 fq->flush_pending_idx ^= 1;
295
296 blk_rq_init(q, flush_rq);
297
298 /*
299 * In case of none scheduler, borrow tag from the first request
300 * since they can't be in flight at the same time. And acquire
301 * the tag's ownership for flush req.
302 *
303 * In case of IO scheduler, flush rq need to borrow scheduler tag
304 * just for cheating put/get driver tag.
305 */
306 flush_rq->mq_ctx = first_rq->mq_ctx;
307 flush_rq->mq_hctx = first_rq->mq_hctx;
308
309 if (!q->elevator) {
310 fq->orig_rq = first_rq;
311 flush_rq->tag = first_rq->tag;
312 blk_mq_tag_set_rq(flush_rq->mq_hctx, first_rq->tag, flush_rq);
313 } else {
314 flush_rq->internal_tag = first_rq->internal_tag;
315 }
316
317 flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
318 flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
319 flush_rq->rq_flags |= RQF_FLUSH_SEQ;
320 flush_rq->rq_disk = first_rq->rq_disk;
321 flush_rq->end_io = flush_end_io;
322
323 blk_flush_queue_rq(flush_rq, false);
324 }
325
mq_flush_data_end_io(struct request * rq,blk_status_t error)326 static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
327 {
328 struct request_queue *q = rq->q;
329 struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
330 struct blk_mq_ctx *ctx = rq->mq_ctx;
331 unsigned long flags;
332 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
333
334 if (q->elevator) {
335 WARN_ON(rq->tag < 0);
336 blk_mq_put_driver_tag(rq);
337 }
338
339 /*
340 * After populating an empty queue, kick it to avoid stall. Read
341 * the comment in flush_end_io().
342 */
343 spin_lock_irqsave(&fq->mq_flush_lock, flags);
344 blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
345 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
346
347 blk_mq_sched_restart(hctx);
348 }
349
350 /**
351 * blk_insert_flush - insert a new PREFLUSH/FUA request
352 * @rq: request to insert
353 *
354 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
355 * or __blk_mq_run_hw_queue() to dispatch request.
356 * @rq is being submitted. Analyze what needs to be done and put it on the
357 * right queue.
358 */
blk_insert_flush(struct request * rq)359 void blk_insert_flush(struct request *rq)
360 {
361 struct request_queue *q = rq->q;
362 unsigned long fflags = q->queue_flags; /* may change, cache */
363 unsigned int policy = blk_flush_policy(fflags, rq);
364 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
365
366 /*
367 * @policy now records what operations need to be done. Adjust
368 * REQ_PREFLUSH and FUA for the driver.
369 */
370 rq->cmd_flags &= ~REQ_PREFLUSH;
371 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
372 rq->cmd_flags &= ~REQ_FUA;
373
374 /*
375 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
376 * of those flags, we have to set REQ_SYNC to avoid skewing
377 * the request accounting.
378 */
379 rq->cmd_flags |= REQ_SYNC;
380
381 /*
382 * An empty flush handed down from a stacking driver may
383 * translate into nothing if the underlying device does not
384 * advertise a write-back cache. In this case, simply
385 * complete the request.
386 */
387 if (!policy) {
388 blk_mq_end_request(rq, 0);
389 return;
390 }
391
392 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
393
394 /*
395 * If there's data but flush is not necessary, the request can be
396 * processed directly without going through flush machinery. Queue
397 * for normal execution.
398 */
399 if ((policy & REQ_FSEQ_DATA) &&
400 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
401 blk_mq_request_bypass_insert(rq, false);
402 return;
403 }
404
405 /*
406 * @rq should go through flush machinery. Mark it part of flush
407 * sequence and submit for further processing.
408 */
409 memset(&rq->flush, 0, sizeof(rq->flush));
410 INIT_LIST_HEAD(&rq->flush.list);
411 rq->rq_flags |= RQF_FLUSH_SEQ;
412 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
413
414 rq->end_io = mq_flush_data_end_io;
415
416 spin_lock_irq(&fq->mq_flush_lock);
417 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
418 spin_unlock_irq(&fq->mq_flush_lock);
419 }
420
421 /**
422 * blkdev_issue_flush - queue a flush
423 * @bdev: blockdev to issue flush for
424 * @gfp_mask: memory allocation flags (for bio_alloc)
425 * @error_sector: error sector
426 *
427 * Description:
428 * Issue a flush for the block device in question. Caller can supply
429 * room for storing the error offset in case of a flush error, if they
430 * wish to.
431 */
blkdev_issue_flush(struct block_device * bdev,gfp_t gfp_mask,sector_t * error_sector)432 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
433 sector_t *error_sector)
434 {
435 struct request_queue *q;
436 struct bio *bio;
437 int ret = 0;
438
439 if (bdev->bd_disk == NULL)
440 return -ENXIO;
441
442 q = bdev_get_queue(bdev);
443 if (!q)
444 return -ENXIO;
445
446 /*
447 * some block devices may not have their queue correctly set up here
448 * (e.g. loop device without a backing file) and so issuing a flush
449 * here will panic. Ensure there is a request function before issuing
450 * the flush.
451 */
452 if (!q->make_request_fn)
453 return -ENXIO;
454
455 bio = bio_alloc(gfp_mask, 0);
456 bio_set_dev(bio, bdev);
457 bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
458
459 ret = submit_bio_wait(bio);
460
461 /*
462 * The driver must store the error location in ->bi_sector, if
463 * it supports it. For non-stacked drivers, this should be
464 * copied from blk_rq_pos(rq).
465 */
466 if (error_sector)
467 *error_sector = bio->bi_iter.bi_sector;
468
469 bio_put(bio);
470 return ret;
471 }
472 EXPORT_SYMBOL(blkdev_issue_flush);
473
blk_alloc_flush_queue(struct request_queue * q,int node,int cmd_size,gfp_t flags)474 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
475 int node, int cmd_size, gfp_t flags)
476 {
477 struct blk_flush_queue *fq;
478 int rq_sz = sizeof(struct request);
479
480 fq = kzalloc_node(sizeof(*fq), flags, node);
481 if (!fq)
482 goto fail;
483
484 spin_lock_init(&fq->mq_flush_lock);
485
486 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
487 fq->flush_rq = kzalloc_node(rq_sz, flags, node);
488 if (!fq->flush_rq)
489 goto fail_rq;
490
491 INIT_LIST_HEAD(&fq->flush_queue[0]);
492 INIT_LIST_HEAD(&fq->flush_queue[1]);
493 INIT_LIST_HEAD(&fq->flush_data_in_flight);
494
495 return fq;
496
497 fail_rq:
498 kfree(fq);
499 fail:
500 return NULL;
501 }
502
blk_free_flush_queue(struct blk_flush_queue * fq)503 void blk_free_flush_queue(struct blk_flush_queue *fq)
504 {
505 /* bio based request queue hasn't flush queue */
506 if (!fq)
507 return;
508
509 kfree(fq->flush_rq);
510 kfree(fq);
511 }
512
