xref: /openbmc/linux/block/blk-flush.c (revision 32981ea5)
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 
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_FLUSH)
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 
115 static unsigned int blk_flush_cur_seq(struct request *rq)
116 {
117 	return 1 << ffz(rq->flush.seq);
118 }
119 
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->cmd_flags &= ~REQ_FLUSH_SEQ;
131 	rq->end_io = rq->flush.saved_end_io;
132 }
133 
134 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
135 {
136 	if (rq->q->mq_ops) {
137 		struct request_queue *q = rq->q;
138 
139 		blk_mq_add_to_requeue_list(rq, add_front);
140 		blk_mq_kick_requeue_list(q);
141 		return false;
142 	} else {
143 		if (add_front)
144 			list_add(&rq->queuelist, &rq->q->queue_head);
145 		else
146 			list_add_tail(&rq->queuelist, &rq->q->queue_head);
147 		return true;
148 	}
149 }
150 
151 /**
152  * blk_flush_complete_seq - complete flush sequence
153  * @rq: FLUSH/FUA request being sequenced
154  * @fq: flush queue
155  * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
156  * @error: whether an error occurred
157  *
158  * @rq just completed @seq part of its flush sequence, record the
159  * completion and trigger the next step.
160  *
161  * CONTEXT:
162  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
163  *
164  * RETURNS:
165  * %true if requests were added to the dispatch queue, %false otherwise.
166  */
167 static bool blk_flush_complete_seq(struct request *rq,
168 				   struct blk_flush_queue *fq,
169 				   unsigned int seq, int error)
170 {
171 	struct request_queue *q = rq->q;
172 	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
173 	bool queued = false, kicked;
174 
175 	BUG_ON(rq->flush.seq & seq);
176 	rq->flush.seq |= seq;
177 
178 	if (likely(!error))
179 		seq = blk_flush_cur_seq(rq);
180 	else
181 		seq = REQ_FSEQ_DONE;
182 
183 	switch (seq) {
184 	case REQ_FSEQ_PREFLUSH:
185 	case REQ_FSEQ_POSTFLUSH:
186 		/* queue for flush */
187 		if (list_empty(pending))
188 			fq->flush_pending_since = jiffies;
189 		list_move_tail(&rq->flush.list, pending);
190 		break;
191 
192 	case REQ_FSEQ_DATA:
193 		list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
194 		queued = blk_flush_queue_rq(rq, true);
195 		break;
196 
197 	case REQ_FSEQ_DONE:
198 		/*
199 		 * @rq was previously adjusted by blk_flush_issue() for
200 		 * flush sequencing and may already have gone through the
201 		 * flush data request completion path.  Restore @rq for
202 		 * normal completion and end it.
203 		 */
204 		BUG_ON(!list_empty(&rq->queuelist));
205 		list_del_init(&rq->flush.list);
206 		blk_flush_restore_request(rq);
207 		if (q->mq_ops)
208 			blk_mq_end_request(rq, error);
209 		else
210 			__blk_end_request_all(rq, error);
211 		break;
212 
213 	default:
214 		BUG();
215 	}
216 
217 	kicked = blk_kick_flush(q, fq);
218 	return kicked | queued;
219 }
220 
221 static void flush_end_io(struct request *flush_rq, int error)
222 {
223 	struct request_queue *q = flush_rq->q;
224 	struct list_head *running;
225 	bool queued = false;
226 	struct request *rq, *n;
227 	unsigned long flags = 0;
228 	struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
229 
230 	if (q->mq_ops) {
231 		struct blk_mq_hw_ctx *hctx;
232 
233 		/* release the tag's ownership to the req cloned from */
234 		spin_lock_irqsave(&fq->mq_flush_lock, flags);
235 		hctx = q->mq_ops->map_queue(q, flush_rq->mq_ctx->cpu);
236 		blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
237 		flush_rq->tag = -1;
238 	}
239 
240 	running = &fq->flush_queue[fq->flush_running_idx];
241 	BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
242 
243 	/* account completion of the flush request */
244 	fq->flush_running_idx ^= 1;
245 
246 	if (!q->mq_ops)
247 		elv_completed_request(q, flush_rq);
248 
249 	/* and push the waiting requests to the next stage */
250 	list_for_each_entry_safe(rq, n, running, flush.list) {
251 		unsigned int seq = blk_flush_cur_seq(rq);
252 
253 		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
254 		queued |= blk_flush_complete_seq(rq, fq, seq, error);
255 	}
256 
257 	/*
258 	 * Kick the queue to avoid stall for two cases:
259 	 * 1. Moving a request silently to empty queue_head may stall the
260 	 * queue.
261 	 * 2. When flush request is running in non-queueable queue, the
262 	 * queue is hold. Restart the queue after flush request is finished
263 	 * to avoid stall.
264 	 * This function is called from request completion path and calling
265 	 * directly into request_fn may confuse the driver.  Always use
266 	 * kblockd.
267 	 */
268 	if (queued || fq->flush_queue_delayed) {
269 		WARN_ON(q->mq_ops);
270 		blk_run_queue_async(q);
271 	}
272 	fq->flush_queue_delayed = 0;
273 	if (q->mq_ops)
274 		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
275 }
276 
277 /**
278  * blk_kick_flush - consider issuing flush request
279  * @q: request_queue being kicked
280  * @fq: flush queue
281  *
282  * Flush related states of @q have changed, consider issuing flush request.
283  * Please read the comment at the top of this file for more info.
284  *
285  * CONTEXT:
286  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
287  *
288  * RETURNS:
289  * %true if flush was issued, %false otherwise.
290  */
291 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
292 {
293 	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
294 	struct request *first_rq =
295 		list_first_entry(pending, struct request, flush.list);
296 	struct request *flush_rq = fq->flush_rq;
297 
298 	/* C1 described at the top of this file */
299 	if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
300 		return false;
301 
302 	/* C2 and C3 */
303 	if (!list_empty(&fq->flush_data_in_flight) &&
304 	    time_before(jiffies,
305 			fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
306 		return false;
307 
308 	/*
309 	 * Issue flush and toggle pending_idx.  This makes pending_idx
310 	 * different from running_idx, which means flush is in flight.
311 	 */
312 	fq->flush_pending_idx ^= 1;
313 
314 	blk_rq_init(q, flush_rq);
315 
316 	/*
317 	 * Borrow tag from the first request since they can't
318 	 * be in flight at the same time. And acquire the tag's
319 	 * ownership for flush req.
320 	 */
321 	if (q->mq_ops) {
322 		struct blk_mq_hw_ctx *hctx;
323 
324 		flush_rq->mq_ctx = first_rq->mq_ctx;
325 		flush_rq->tag = first_rq->tag;
326 		fq->orig_rq = first_rq;
327 
328 		hctx = q->mq_ops->map_queue(q, first_rq->mq_ctx->cpu);
329 		blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
330 	}
331 
332 	flush_rq->cmd_type = REQ_TYPE_FS;
333 	flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
334 	flush_rq->rq_disk = first_rq->rq_disk;
335 	flush_rq->end_io = flush_end_io;
336 
337 	return blk_flush_queue_rq(flush_rq, false);
338 }
339 
340 static void flush_data_end_io(struct request *rq, int error)
341 {
342 	struct request_queue *q = rq->q;
343 	struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
344 
345 	/*
346 	 * After populating an empty queue, kick it to avoid stall.  Read
347 	 * the comment in flush_end_io().
348 	 */
349 	if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
350 		blk_run_queue_async(q);
351 }
352 
353 static void mq_flush_data_end_io(struct request *rq, int error)
354 {
355 	struct request_queue *q = rq->q;
356 	struct blk_mq_hw_ctx *hctx;
357 	struct blk_mq_ctx *ctx = rq->mq_ctx;
358 	unsigned long flags;
359 	struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
360 
361 	hctx = q->mq_ops->map_queue(q, ctx->cpu);
362 
363 	/*
364 	 * After populating an empty queue, kick it to avoid stall.  Read
365 	 * the comment in flush_end_io().
366 	 */
367 	spin_lock_irqsave(&fq->mq_flush_lock, flags);
368 	if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
369 		blk_mq_run_hw_queue(hctx, true);
370 	spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
371 }
372 
373 /**
374  * blk_insert_flush - insert a new FLUSH/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  *
382  * CONTEXT:
383  * spin_lock_irq(q->queue_lock) in !mq case
384  */
385 void blk_insert_flush(struct request *rq)
386 {
387 	struct request_queue *q = rq->q;
388 	unsigned long fflags = q->queue_flags;	/* may change, cache */
389 	unsigned int policy = blk_flush_policy(fflags, rq);
390 	struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
391 
392 	/*
393 	 * @policy now records what operations need to be done.  Adjust
394 	 * REQ_FLUSH and FUA for the driver.
395 	 */
396 	rq->cmd_flags &= ~REQ_FLUSH;
397 	if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
398 		rq->cmd_flags &= ~REQ_FUA;
399 
400 	/*
401 	 * An empty flush handed down from a stacking driver may
402 	 * translate into nothing if the underlying device does not
403 	 * advertise a write-back cache.  In this case, simply
404 	 * complete the request.
405 	 */
406 	if (!policy) {
407 		if (q->mq_ops)
408 			blk_mq_end_request(rq, 0);
409 		else
410 			__blk_end_bidi_request(rq, 0, 0, 0);
411 		return;
412 	}
413 
414 	BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
415 
416 	/*
417 	 * If there's data but flush is not necessary, the request can be
418 	 * processed directly without going through flush machinery.  Queue
419 	 * for normal execution.
420 	 */
421 	if ((policy & REQ_FSEQ_DATA) &&
422 	    !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
423 		if (q->mq_ops) {
424 			blk_mq_insert_request(rq, false, false, true);
425 		} else
426 			list_add_tail(&rq->queuelist, &q->queue_head);
427 		return;
428 	}
429 
430 	/*
431 	 * @rq should go through flush machinery.  Mark it part of flush
432 	 * sequence and submit for further processing.
433 	 */
434 	memset(&rq->flush, 0, sizeof(rq->flush));
435 	INIT_LIST_HEAD(&rq->flush.list);
436 	rq->cmd_flags |= REQ_FLUSH_SEQ;
437 	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
438 	if (q->mq_ops) {
439 		rq->end_io = mq_flush_data_end_io;
440 
441 		spin_lock_irq(&fq->mq_flush_lock);
442 		blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
443 		spin_unlock_irq(&fq->mq_flush_lock);
444 		return;
445 	}
446 	rq->end_io = flush_data_end_io;
447 
448 	blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
449 }
450 
451 /**
452  * blkdev_issue_flush - queue a flush
453  * @bdev:	blockdev to issue flush for
454  * @gfp_mask:	memory allocation flags (for bio_alloc)
455  * @error_sector:	error sector
456  *
457  * Description:
458  *    Issue a flush for the block device in question. Caller can supply
459  *    room for storing the error offset in case of a flush error, if they
460  *    wish to. If WAIT flag is not passed then caller may check only what
461  *    request was pushed in some internal queue for later handling.
462  */
463 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
464 		sector_t *error_sector)
465 {
466 	struct request_queue *q;
467 	struct bio *bio;
468 	int ret = 0;
469 
470 	if (bdev->bd_disk == NULL)
471 		return -ENXIO;
472 
473 	q = bdev_get_queue(bdev);
474 	if (!q)
475 		return -ENXIO;
476 
477 	/*
478 	 * some block devices may not have their queue correctly set up here
479 	 * (e.g. loop device without a backing file) and so issuing a flush
480 	 * here will panic. Ensure there is a request function before issuing
481 	 * the flush.
482 	 */
483 	if (!q->make_request_fn)
484 		return -ENXIO;
485 
486 	bio = bio_alloc(gfp_mask, 0);
487 	bio->bi_bdev = bdev;
488 
489 	ret = submit_bio_wait(WRITE_FLUSH, bio);
490 
491 	/*
492 	 * The driver must store the error location in ->bi_sector, if
493 	 * it supports it. For non-stacked drivers, this should be
494 	 * copied from blk_rq_pos(rq).
495 	 */
496 	if (error_sector)
497 		*error_sector = bio->bi_iter.bi_sector;
498 
499 	bio_put(bio);
500 	return ret;
501 }
502 EXPORT_SYMBOL(blkdev_issue_flush);
503 
504 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
505 		int node, int cmd_size)
506 {
507 	struct blk_flush_queue *fq;
508 	int rq_sz = sizeof(struct request);
509 
510 	fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
511 	if (!fq)
512 		goto fail;
513 
514 	if (q->mq_ops) {
515 		spin_lock_init(&fq->mq_flush_lock);
516 		rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
517 	}
518 
519 	fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
520 	if (!fq->flush_rq)
521 		goto fail_rq;
522 
523 	INIT_LIST_HEAD(&fq->flush_queue[0]);
524 	INIT_LIST_HEAD(&fq->flush_queue[1]);
525 	INIT_LIST_HEAD(&fq->flush_data_in_flight);
526 
527 	return fq;
528 
529  fail_rq:
530 	kfree(fq);
531  fail:
532 	return NULL;
533 }
534 
535 void blk_free_flush_queue(struct blk_flush_queue *fq)
536 {
537 	/* bio based request queue hasn't flush queue */
538 	if (!fq)
539 		return;
540 
541 	kfree(fq->flush_rq);
542 	kfree(fq);
543 }
544