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