Branch data 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/blk-mq.h>
72 : : #include <linux/lockdep.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 */
80 : : enum {
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 : :
96 : : static void blk_kick_flush(struct request_queue *q,
97 : : struct blk_flush_queue *fq, unsigned int flags);
98 : :
99 : 0 : static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
100 : : {
101 : : unsigned int policy = 0;
102 : :
103 [ # # ]: 0 : if (blk_rq_sectors(rq))
104 : : policy |= REQ_FSEQ_DATA;
105 : :
106 [ # # ]: 0 : if (fflags & (1UL << QUEUE_FLAG_WC)) {
107 [ # # ]: 0 : if (rq->cmd_flags & REQ_PREFLUSH)
108 : 0 : policy |= REQ_FSEQ_PREFLUSH;
109 [ # # # # ]: 0 : if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
110 : 0 : (rq->cmd_flags & REQ_FUA))
111 : 0 : policy |= REQ_FSEQ_POSTFLUSH;
112 : : }
113 : 0 : return policy;
114 : : }
115 : :
116 : : static unsigned int blk_flush_cur_seq(struct request *rq)
117 : : {
118 : 0 : return 1 << ffz(rq->flush.seq);
119 : : }
120 : :
121 : : static 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 : 0 : rq->bio = rq->biotail;
129 : :
130 : : /* make @rq a normal request */
131 : 0 : rq->rq_flags &= ~RQF_FLUSH_SEQ;
132 : 0 : rq->end_io = rq->flush.saved_end_io;
133 : : }
134 : :
135 : : static void blk_flush_queue_rq(struct request *rq, bool add_front)
136 : : {
137 : 0 : blk_mq_add_to_requeue_list(rq, add_front, true);
138 : : }
139 : :
140 : : /**
141 : : * blk_flush_complete_seq - complete flush sequence
142 : : * @rq: PREFLUSH/FUA request being sequenced
143 : : * @fq: flush queue
144 : : * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
145 : : * @error: whether an error occurred
146 : : *
147 : : * @rq just completed @seq part of its flush sequence, record the
148 : : * completion and trigger the next step.
149 : : *
150 : : * CONTEXT:
151 : : * spin_lock_irq(fq->mq_flush_lock)
152 : : *
153 : : * RETURNS:
154 : : * %true if requests were added to the dispatch queue, %false otherwise.
155 : : */
156 : 0 : static void blk_flush_complete_seq(struct request *rq,
157 : : struct blk_flush_queue *fq,
158 : : unsigned int seq, blk_status_t error)
159 : : {
160 : 0 : struct request_queue *q = rq->q;
161 : 0 : struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
162 : : unsigned int cmd_flags;
163 : :
164 [ # # ]: 0 : BUG_ON(rq->flush.seq & seq);
165 : 0 : rq->flush.seq |= seq;
166 : 0 : cmd_flags = rq->cmd_flags;
167 : :
168 [ # # ]: 0 : if (likely(!error))
169 : : seq = blk_flush_cur_seq(rq);
170 : : else
171 : : seq = REQ_FSEQ_DONE;
172 : :
173 [ # # # # ]: 0 : switch (seq) {
174 : : case REQ_FSEQ_PREFLUSH:
175 : : case REQ_FSEQ_POSTFLUSH:
176 : : /* queue for flush */
177 [ # # ]: 0 : if (list_empty(pending))
178 : 0 : fq->flush_pending_since = jiffies;
179 : 0 : list_move_tail(&rq->flush.list, pending);
180 : : break;
181 : :
182 : : case REQ_FSEQ_DATA:
183 : 0 : list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
184 : : blk_flush_queue_rq(rq, true);
185 : : break;
186 : :
187 : : case REQ_FSEQ_DONE:
188 : : /*
189 : : * @rq was previously adjusted by blk_flush_issue() for
190 : : * flush sequencing and may already have gone through the
191 : : * flush data request completion path. Restore @rq for
192 : : * normal completion and end it.
193 : : */
194 [ # # ]: 0 : BUG_ON(!list_empty(&rq->queuelist));
195 : 0 : list_del_init(&rq->flush.list);
196 : : blk_flush_restore_request(rq);
197 : 0 : blk_mq_end_request(rq, error);
198 : 0 : break;
199 : :
200 : : default:
201 : 0 : BUG();
202 : : }
203 : :
204 : 0 : blk_kick_flush(q, fq, cmd_flags);
205 : 0 : }
206 : :
207 : 0 : static void flush_end_io(struct request *flush_rq, blk_status_t error)
208 : : {
209 : 0 : struct request_queue *q = flush_rq->q;
210 : : struct list_head *running;
211 : : struct request *rq, *n;
212 : : unsigned long flags = 0;
213 : 0 : struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
214 : : struct blk_mq_hw_ctx *hctx;
215 : :
216 : : /* release the tag's ownership to the req cloned from */
217 : 0 : spin_lock_irqsave(&fq->mq_flush_lock, flags);
218 : :
219 [ # # ]: 0 : if (!refcount_dec_and_test(&flush_rq->ref)) {
220 : 0 : fq->rq_status = error;
221 : : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
222 : 0 : return;
223 : : }
224 : :
225 [ # # ]: 0 : if (fq->rq_status != BLK_STS_OK)
226 : : error = fq->rq_status;
227 : :
228 : 0 : hctx = flush_rq->mq_hctx;
229 [ # # ]: 0 : if (!q->elevator) {
230 : 0 : blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
231 : 0 : flush_rq->tag = -1;
232 : : } else {
233 : 0 : blk_mq_put_driver_tag(flush_rq);
234 : 0 : flush_rq->internal_tag = -1;
235 : : }
236 : :
237 : 0 : running = &fq->flush_queue[fq->flush_running_idx];
238 [ # # ]: 0 : BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
239 : :
240 : : /* account completion of the flush request */
241 : 0 : fq->flush_running_idx ^= 1;
242 : :
243 : : /* and push the waiting requests to the next stage */
244 [ # # ]: 0 : list_for_each_entry_safe(rq, n, running, flush.list) {
245 : : unsigned int seq = blk_flush_cur_seq(rq);
246 : :
247 [ # # ]: 0 : BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
248 : 0 : blk_flush_complete_seq(rq, fq, seq, error);
249 : : }
250 : :
251 : 0 : fq->flush_queue_delayed = 0;
252 : : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
253 : : }
254 : :
255 : : /**
256 : : * blk_kick_flush - consider issuing flush request
257 : : * @q: request_queue being kicked
258 : : * @fq: flush queue
259 : : * @flags: cmd_flags of the original request
260 : : *
261 : : * Flush related states of @q have changed, consider issuing flush request.
262 : : * Please read the comment at the top of this file for more info.
263 : : *
264 : : * CONTEXT:
265 : : * spin_lock_irq(fq->mq_flush_lock)
266 : : *
267 : : */
268 : 0 : static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
269 : : unsigned int flags)
270 : : {
271 : 0 : struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
272 : : struct request *first_rq =
273 : 0 : list_first_entry(pending, struct request, flush.list);
274 : 0 : struct request *flush_rq = fq->flush_rq;
275 : :
276 : : /* C1 described at the top of this file */
277 [ # # # # ]: 0 : if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
278 : : return;
279 : :
280 : : /* C2 and C3
281 : : *
282 : : * For blk-mq + scheduling, we can risk having all driver tags
283 : : * assigned to empty flushes, and we deadlock if we are expecting
284 : : * other requests to make progress. Don't defer for that case.
285 : : */
286 [ # # # # ]: 0 : if (!list_empty(&fq->flush_data_in_flight) && q->elevator &&
287 [ # # ]: 0 : time_before(jiffies,
288 : : fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
289 : : return;
290 : :
291 : : /*
292 : : * Issue flush and toggle pending_idx. This makes pending_idx
293 : : * different from running_idx, which means flush is in flight.
294 : : */
295 : 0 : fq->flush_pending_idx ^= 1;
296 : :
297 : 0 : blk_rq_init(q, flush_rq);
298 : :
299 : : /*
300 : : * In case of none scheduler, borrow tag from the first request
301 : : * since they can't be in flight at the same time. And acquire
302 : : * the tag's ownership for flush req.
303 : : *
304 : : * In case of IO scheduler, flush rq need to borrow scheduler tag
305 : : * just for cheating put/get driver tag.
306 : : */
307 : 0 : flush_rq->mq_ctx = first_rq->mq_ctx;
308 : 0 : flush_rq->mq_hctx = first_rq->mq_hctx;
309 : :
310 [ # # ]: 0 : if (!q->elevator) {
311 : 0 : fq->orig_rq = first_rq;
312 : 0 : flush_rq->tag = first_rq->tag;
313 : 0 : blk_mq_tag_set_rq(flush_rq->mq_hctx, first_rq->tag, flush_rq);
314 : : } else {
315 : 0 : flush_rq->internal_tag = first_rq->internal_tag;
316 : : }
317 : :
318 : 0 : flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
319 : 0 : flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
320 : 0 : flush_rq->rq_flags |= RQF_FLUSH_SEQ;
321 : 0 : flush_rq->rq_disk = first_rq->rq_disk;
322 : 0 : flush_rq->end_io = flush_end_io;
323 : :
324 : : blk_flush_queue_rq(flush_rq, false);
325 : : }
326 : :
327 : 0 : static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
328 : : {
329 : 0 : struct request_queue *q = rq->q;
330 : 0 : struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
331 : 0 : struct blk_mq_ctx *ctx = rq->mq_ctx;
332 : : unsigned long flags;
333 : : struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
334 : :
335 [ # # ]: 0 : if (q->elevator) {
336 [ # # ]: 0 : WARN_ON(rq->tag < 0);
337 : 0 : blk_mq_put_driver_tag(rq);
338 : : }
339 : :
340 : : /*
341 : : * After populating an empty queue, kick it to avoid stall. Read
342 : : * the comment in flush_end_io().
343 : : */
344 : 0 : spin_lock_irqsave(&fq->mq_flush_lock, flags);
345 : 0 : blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
346 : : spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
347 : :
348 : 0 : blk_mq_sched_restart(hctx);
349 : 0 : }
350 : :
351 : : /**
352 : : * blk_insert_flush - insert a new PREFLUSH/FUA request
353 : : * @rq: request to insert
354 : : *
355 : : * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
356 : : * or __blk_mq_run_hw_queue() to dispatch request.
357 : : * @rq is being submitted. Analyze what needs to be done and put it on the
358 : : * right queue.
359 : : */
360 : 0 : void blk_insert_flush(struct request *rq)
361 : : {
362 : 0 : struct request_queue *q = rq->q;
363 : 0 : unsigned long fflags = q->queue_flags; /* may change, cache */
364 : 0 : unsigned int policy = blk_flush_policy(fflags, rq);
365 : 0 : struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
366 : :
367 : : /*
368 : : * @policy now records what operations need to be done. Adjust
369 : : * REQ_PREFLUSH and FUA for the driver.
370 : : */
371 : 0 : rq->cmd_flags &= ~REQ_PREFLUSH;
372 [ # # ]: 0 : if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
373 : 0 : rq->cmd_flags &= ~REQ_FUA;
374 : :
375 : : /*
376 : : * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
377 : : * of those flags, we have to set REQ_SYNC to avoid skewing
378 : : * the request accounting.
379 : : */
380 : 0 : rq->cmd_flags |= REQ_SYNC;
381 : :
382 : : /*
383 : : * An empty flush handed down from a stacking driver may
384 : : * translate into nothing if the underlying device does not
385 : : * advertise a write-back cache. In this case, simply
386 : : * complete the request.
387 : : */
388 [ # # ]: 0 : if (!policy) {
389 : 0 : blk_mq_end_request(rq, 0);
390 : 0 : return;
391 : : }
392 : :
393 [ # # ]: 0 : BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
394 : :
395 : : /*
396 : : * If there's data but flush is not necessary, the request can be
397 : : * processed directly without going through flush machinery. Queue
398 : : * for normal execution.
399 : : */
400 [ # # ]: 0 : if ((policy & REQ_FSEQ_DATA) &&
401 : : !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
402 : 0 : blk_mq_request_bypass_insert(rq, false, false);
403 : 0 : return;
404 : : }
405 : :
406 : : /*
407 : : * @rq should go through flush machinery. Mark it part of flush
408 : : * sequence and submit for further processing.
409 : : */
410 : 0 : memset(&rq->flush, 0, sizeof(rq->flush));
411 : 0 : INIT_LIST_HEAD(&rq->flush.list);
412 : 0 : rq->rq_flags |= RQF_FLUSH_SEQ;
413 : 0 : rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
414 : :
415 : 0 : rq->end_io = mq_flush_data_end_io;
416 : :
417 : : spin_lock_irq(&fq->mq_flush_lock);
418 : 0 : blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
419 : : spin_unlock_irq(&fq->mq_flush_lock);
420 : : }
421 : :
422 : : /**
423 : : * blkdev_issue_flush - queue a flush
424 : : * @bdev: blockdev to issue flush for
425 : : * @gfp_mask: memory allocation flags (for bio_alloc)
426 : : * @error_sector: error sector
427 : : *
428 : : * Description:
429 : : * Issue a flush for the block device in question. Caller can supply
430 : : * room for storing the error offset in case of a flush error, if they
431 : : * wish to.
432 : : */
433 : 1163 : int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
434 : : sector_t *error_sector)
435 : : {
436 : : struct request_queue *q;
437 : : struct bio *bio;
438 : : int ret = 0;
439 : :
440 [ + - ]: 1163 : if (bdev->bd_disk == NULL)
441 : : return -ENXIO;
442 : :
443 : : q = bdev_get_queue(bdev);
444 [ + - ]: 1163 : if (!q)
445 : : return -ENXIO;
446 : :
447 : : /*
448 : : * some block devices may not have their queue correctly set up here
449 : : * (e.g. loop device without a backing file) and so issuing a flush
450 : : * here will panic. Ensure there is a request function before issuing
451 : : * the flush.
452 : : */
453 [ + - ]: 1163 : if (!q->make_request_fn)
454 : : return -ENXIO;
455 : :
456 : : bio = bio_alloc(gfp_mask, 0);
457 [ + - ]: 2326 : bio_set_dev(bio, bdev);
458 : 1163 : bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
459 : :
460 : 1163 : ret = submit_bio_wait(bio);
461 : :
462 : : /*
463 : : * The driver must store the error location in ->bi_sector, if
464 : : * it supports it. For non-stacked drivers, this should be
465 : : * copied from blk_rq_pos(rq).
466 : : */
467 [ - + ]: 1163 : if (error_sector)
468 : 0 : *error_sector = bio->bi_iter.bi_sector;
469 : :
470 : 1163 : bio_put(bio);
471 : 1163 : return ret;
472 : : }
473 : : EXPORT_SYMBOL(blkdev_issue_flush);
474 : :
475 : 1863 : struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
476 : : int node, int cmd_size, gfp_t flags)
477 : : {
478 : : struct blk_flush_queue *fq;
479 : : int rq_sz = sizeof(struct request);
480 : :
481 : 1863 : fq = kzalloc_node(sizeof(*fq), flags, node);
482 [ + - ]: 1863 : if (!fq)
483 : : goto fail;
484 : :
485 : 1863 : spin_lock_init(&fq->mq_flush_lock);
486 : :
487 : 1863 : rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
488 : 1863 : fq->flush_rq = kzalloc_node(rq_sz, flags, node);
489 [ + - ]: 1863 : if (!fq->flush_rq)
490 : : goto fail_rq;
491 : :
492 : 1863 : INIT_LIST_HEAD(&fq->flush_queue[0]);
493 : 1863 : INIT_LIST_HEAD(&fq->flush_queue[1]);
494 : 1863 : INIT_LIST_HEAD(&fq->flush_data_in_flight);
495 : :
496 : : lockdep_register_key(&fq->key);
497 : : lockdep_set_class(&fq->mq_flush_lock, &fq->key);
498 : :
499 : 1863 : return fq;
500 : :
501 : : fail_rq:
502 : 0 : kfree(fq);
503 : : fail:
504 : : return NULL;
505 : : }
506 : :
507 : 0 : void blk_free_flush_queue(struct blk_flush_queue *fq)
508 : : {
509 : : /* bio based request queue hasn't flush queue */
510 [ # # ]: 0 : if (!fq)
511 : 0 : return;
512 : :
513 : : lockdep_unregister_key(&fq->key);
514 : 0 : kfree(fq->flush_rq);
515 : 0 : kfree(fq);
516 : : }
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