1 /*
2 * Functions to sequence FLUSH 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_{FLUSH|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_FLUSH makes sense, which
14 * indicates a simple flush request. If there is data, REQ_FLUSH 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, FLUSH and FUA don't make any
20 * difference. The requests are either completed immediately if there's no
21 * data or executed as normal requests otherwise.
22 *
23 * If the device has writeback cache and supports FUA, REQ_FLUSH 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_FLUSH is
27 * 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 * 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 FLUSH/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 FLUSH) 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 FLUSH/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 REQ_FLUSH_SEQ in
60 * req_bio_endio().
61 *
62 * The above peculiarity requires that each FLUSH/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
78 /* FLUSH/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 bool blk_kick_flush(struct request_queue *q,
96 struct blk_flush_queue *fq);
97
blk_flush_policy(unsigned int fflags,struct request * rq)98 static unsigned int blk_flush_policy(unsigned int 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 & REQ_FLUSH) {
106 if (rq->cmd_flags & REQ_FLUSH)
107 policy |= REQ_FSEQ_PREFLUSH;
108 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
109 policy |= REQ_FSEQ_POSTFLUSH;
110 }
111 return policy;
112 }
113
blk_flush_cur_seq(struct request * rq)114 static unsigned int blk_flush_cur_seq(struct request *rq)
115 {
116 return 1 << ffz(rq->flush.seq);
117 }
118
blk_flush_restore_request(struct request * rq)119 static void blk_flush_restore_request(struct request *rq)
120 {
121 /*
122 * After flush data completion, @rq->bio is %NULL but we need to
123 * complete the bio again. @rq->biotail is guaranteed to equal the
124 * original @rq->bio. Restore it.
125 */
126 rq->bio = rq->biotail;
127
128 /* make @rq a normal request */
129 rq->cmd_flags &= ~REQ_FLUSH_SEQ;
130 rq->end_io = rq->flush.saved_end_io;
131 }
132
blk_flush_queue_rq(struct request * rq,bool add_front)133 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
134 {
135 if (rq->q->mq_ops) {
136 struct request_queue *q = rq->q;
137
138 blk_mq_add_to_requeue_list(rq, add_front);
139 blk_mq_kick_requeue_list(q);
140 return false;
141 } else {
142 if (add_front)
143 list_add(&rq->queuelist, &rq->q->queue_head);
144 else
145 list_add_tail(&rq->queuelist, &rq->q->queue_head);
146 return true;
147 }
148 }
149
150 /**
151 * blk_flush_complete_seq - complete flush sequence
152 * @rq: FLUSH/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(q->queue_lock or fq->mq_flush_lock)
162 *
163 * RETURNS:
164 * %true if requests were added to the dispatch queue, %false otherwise.
165 */
blk_flush_complete_seq(struct request * rq,struct blk_flush_queue * fq,unsigned int seq,int error)166 static bool blk_flush_complete_seq(struct request *rq,
167 struct blk_flush_queue *fq,
168 unsigned int seq, int error)
169 {
170 struct request_queue *q = rq->q;
171 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
172 bool queued = false, kicked;
173
174 BUG_ON(rq->flush.seq & seq);
175 rq->flush.seq |= seq;
176
177 if (likely(!error))
178 seq = blk_flush_cur_seq(rq);
179 else
180 seq = REQ_FSEQ_DONE;
181
182 switch (seq) {
183 case REQ_FSEQ_PREFLUSH:
184 case REQ_FSEQ_POSTFLUSH:
185 /* queue for flush */
186 if (list_empty(pending))
187 fq->flush_pending_since = jiffies;
188 list_move_tail(&rq->flush.list, pending);
189 break;
190
191 case REQ_FSEQ_DATA:
192 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
193 queued = blk_flush_queue_rq(rq, true);
194 break;
195
196 case REQ_FSEQ_DONE:
197 /*
198 * @rq was previously adjusted by blk_flush_issue() for
199 * flush sequencing and may already have gone through the
200 * flush data request completion path. Restore @rq for
201 * normal completion and end it.
202 */
203 BUG_ON(!list_empty(&rq->queuelist));
204 list_del_init(&rq->flush.list);
205 blk_flush_restore_request(rq);
206 if (q->mq_ops)
207 blk_mq_end_request(rq, error);
208 else
209 __blk_end_request_all(rq, error);
210 break;
211
212 default:
213 BUG();
214 }
215
216 kicked = blk_kick_flush(q, fq);
217 return kicked | queued;
218 }
219
flush_end_io(struct request * flush_rq,int error)220 static void flush_end_io(struct request *flush_rq, int error)
221 {
222 struct request_queue *q = flush_rq->q;
223 struct list_head *running;
224 bool queued = false;
225 struct request *rq, *n;
226 unsigned long flags = 0;
227 struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
228
229 if (q->mq_ops) {
230 struct blk_mq_hw_ctx *hctx;
231
232 /* release the tag's ownership to the req cloned from */
233 spin_lock_irqsave(&fq->mq_flush_lock, flags);
234 hctx = q->mq_ops->map_queue(q, flush_rq->mq_ctx->cpu);
235 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
236 flush_rq->tag = -1;
237 }
238
239 running = &fq->flush_queue[fq->flush_running_idx];
240 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
241
242 /* account completion of the flush request */
243 fq->flush_running_idx ^= 1;
244
245 if (!q->mq_ops)
246 elv_completed_request(q, flush_rq);
247
248 /* and push the waiting requests to the next stage */
249 list_for_each_entry_safe(rq, n, running, flush.list) {
250 unsigned int seq = blk_flush_cur_seq(rq);
251
252 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
253 queued |= blk_flush_complete_seq(rq, fq, seq, error);
254 }
255
256 /*
257 * Kick the queue to avoid stall for two cases:
258 * 1. Moving a request silently to empty queue_head may stall the
259 * queue.
260 * 2. When flush request is running in non-queueable queue, the
261 * queue is hold. Restart the queue after flush request is finished
262 * to avoid stall.
263 * This function is called from request completion path and calling
264 * directly into request_fn may confuse the driver. Always use
265 * kblockd.
266 */
267 if (queued || fq->flush_queue_delayed) {
268 WARN_ON(q->mq_ops);
269 blk_run_queue_async(q);
270 }
271 fq->flush_queue_delayed = 0;
272 if (q->mq_ops)
273 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
274 }
275
276 /**
277 * blk_kick_flush - consider issuing flush request
278 * @q: request_queue being kicked
279 * @fq: flush queue
280 *
281 * Flush related states of @q have changed, consider issuing flush request.
282 * Please read the comment at the top of this file for more info.
283 *
284 * CONTEXT:
285 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
286 *
287 * RETURNS:
288 * %true if flush was issued, %false otherwise.
289 */
blk_kick_flush(struct request_queue * q,struct blk_flush_queue * fq)290 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
291 {
292 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
293 struct request *first_rq =
294 list_first_entry(pending, struct request, flush.list);
295 struct request *flush_rq = fq->flush_rq;
296
297 /* C1 described at the top of this file */
298 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
299 return false;
300
301 /* C2 and C3 */
302 if (!list_empty(&fq->flush_data_in_flight) &&
303 time_before(jiffies,
304 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
305 return false;
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 fq->flush_pending_idx ^= 1;
312
313 blk_rq_init(q, flush_rq);
314
315 /*
316 * Borrow tag from the first request since they can't
317 * be in flight at the same time. And acquire the tag's
318 * ownership for flush req.
319 */
320 if (q->mq_ops) {
321 struct blk_mq_hw_ctx *hctx;
322
323 flush_rq->mq_ctx = first_rq->mq_ctx;
324 flush_rq->tag = first_rq->tag;
325 fq->orig_rq = first_rq;
326
327 hctx = q->mq_ops->map_queue(q, first_rq->mq_ctx->cpu);
328 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
329 }
330
331 flush_rq->cmd_type = REQ_TYPE_FS;
332 flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
333 flush_rq->rq_disk = first_rq->rq_disk;
334 flush_rq->end_io = flush_end_io;
335
336 return blk_flush_queue_rq(flush_rq, false);
337 }
338
flush_data_end_io(struct request * rq,int error)339 static void flush_data_end_io(struct request *rq, int error)
340 {
341 struct request_queue *q = rq->q;
342 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
343
344 /*
345 * After populating an empty queue, kick it to avoid stall. Read
346 * the comment in flush_end_io().
347 */
348 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
349 blk_run_queue_async(q);
350 }
351
mq_flush_data_end_io(struct request * rq,int error)352 static void mq_flush_data_end_io(struct request *rq, int error)
353 {
354 struct request_queue *q = rq->q;
355 struct blk_mq_hw_ctx *hctx;
356 struct blk_mq_ctx *ctx = rq->mq_ctx;
357 unsigned long flags;
358 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
359
360 hctx = q->mq_ops->map_queue(q, ctx->cpu);
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 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
368 blk_mq_run_hw_queue(hctx, true);
369 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
370 }
371
372 /**
373 * blk_insert_flush - insert a new FLUSH/FUA request
374 * @rq: request to insert
375 *
376 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
377 * or __blk_mq_run_hw_queue() to dispatch request.
378 * @rq is being submitted. Analyze what needs to be done and put it on the
379 * right queue.
380 *
381 * CONTEXT:
382 * spin_lock_irq(q->queue_lock) in !mq case
383 */
blk_insert_flush(struct request * rq)384 void blk_insert_flush(struct request *rq)
385 {
386 struct request_queue *q = rq->q;
387 unsigned int fflags = q->flush_flags; /* may change, cache */
388 unsigned int policy = blk_flush_policy(fflags, rq);
389 struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
390
391 /*
392 * @policy now records what operations need to be done. Adjust
393 * REQ_FLUSH and FUA for the driver.
394 */
395 rq->cmd_flags &= ~REQ_FLUSH;
396 if (!(fflags & REQ_FUA))
397 rq->cmd_flags &= ~REQ_FUA;
398
399 /*
400 * An empty flush handed down from a stacking driver may
401 * translate into nothing if the underlying device does not
402 * advertise a write-back cache. In this case, simply
403 * complete the request.
404 */
405 if (!policy) {
406 if (q->mq_ops)
407 blk_mq_end_request(rq, 0);
408 else
409 __blk_end_bidi_request(rq, 0, 0, 0);
410 return;
411 }
412
413 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
414
415 /*
416 * If there's data but flush is not necessary, the request can be
417 * processed directly without going through flush machinery. Queue
418 * for normal execution.
419 */
420 if ((policy & REQ_FSEQ_DATA) &&
421 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
422 if (q->mq_ops) {
423 blk_mq_insert_request(rq, false, false, true);
424 } else
425 list_add_tail(&rq->queuelist, &q->queue_head);
426 return;
427 }
428
429 /*
430 * @rq should go through flush machinery. Mark it part of flush
431 * sequence and submit for further processing.
432 */
433 memset(&rq->flush, 0, sizeof(rq->flush));
434 INIT_LIST_HEAD(&rq->flush.list);
435 rq->cmd_flags |= REQ_FLUSH_SEQ;
436 rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
437 if (q->mq_ops) {
438 rq->end_io = mq_flush_data_end_io;
439
440 spin_lock_irq(&fq->mq_flush_lock);
441 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
442 spin_unlock_irq(&fq->mq_flush_lock);
443 return;
444 }
445 rq->end_io = flush_data_end_io;
446
447 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
448 }
449
450 /**
451 * blkdev_issue_flush - queue a flush
452 * @bdev: blockdev to issue flush for
453 * @gfp_mask: memory allocation flags (for bio_alloc)
454 * @error_sector: error sector
455 *
456 * Description:
457 * Issue a flush for the block device in question. Caller can supply
458 * room for storing the error offset in case of a flush error, if they
459 * wish to. If WAIT flag is not passed then caller may check only what
460 * request was pushed in some internal queue for later handling.
461 */
blkdev_issue_flush(struct block_device * bdev,gfp_t gfp_mask,sector_t * error_sector)462 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
463 sector_t *error_sector)
464 {
465 struct request_queue *q;
466 struct bio *bio;
467 int ret = 0;
468
469 if (bdev->bd_disk == NULL)
470 return -ENXIO;
471
472 q = bdev_get_queue(bdev);
473 if (!q)
474 return -ENXIO;
475
476 /*
477 * some block devices may not have their queue correctly set up here
478 * (e.g. loop device without a backing file) and so issuing a flush
479 * here will panic. Ensure there is a request function before issuing
480 * the flush.
481 */
482 if (!q->make_request_fn)
483 return -ENXIO;
484
485 bio = bio_alloc(gfp_mask, 0);
486 bio->bi_bdev = bdev;
487
488 ret = submit_bio_wait(WRITE_FLUSH, bio);
489
490 /*
491 * The driver must store the error location in ->bi_sector, if
492 * it supports it. For non-stacked drivers, this should be
493 * copied from blk_rq_pos(rq).
494 */
495 if (error_sector)
496 *error_sector = bio->bi_iter.bi_sector;
497
498 bio_put(bio);
499 return ret;
500 }
501 EXPORT_SYMBOL(blkdev_issue_flush);
502
blk_alloc_flush_queue(struct request_queue * q,int node,int cmd_size)503 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
504 int node, int cmd_size)
505 {
506 struct blk_flush_queue *fq;
507 int rq_sz = sizeof(struct request);
508
509 fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
510 if (!fq)
511 goto fail;
512
513 if (q->mq_ops) {
514 spin_lock_init(&fq->mq_flush_lock);
515 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
516 }
517
518 fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
519 if (!fq->flush_rq)
520 goto fail_rq;
521
522 INIT_LIST_HEAD(&fq->flush_queue[0]);
523 INIT_LIST_HEAD(&fq->flush_queue[1]);
524 INIT_LIST_HEAD(&fq->flush_data_in_flight);
525
526 return fq;
527
528 fail_rq:
529 kfree(fq);
530 fail:
531 return NULL;
532 }
533
blk_free_flush_queue(struct blk_flush_queue * fq)534 void blk_free_flush_queue(struct blk_flush_queue *fq)
535 {
536 /* bio based request queue hasn't flush queue */
537 if (!fq)
538 return;
539
540 kfree(fq->flush_rq);
541 kfree(fq);
542 }
543