2 * Functions to sequence FLUSH and FUA writes.
4 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics
5 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>
7 * This file is released under the GPLv2.
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.
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
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.
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.
26 * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
27 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
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 FLUSH/FUA
37 * Currently, the following conditions are used to determine when to issue
40 * C1. At any given time, only one flush shall be in progress. This makes
41 * double buffering sufficient.
43 * C2. Flush is deferred if any request is executing DATA of its sequence.
44 * This avoids issuing separate POSTFLUSHes for requests which shared
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.
52 * For devices which support FUA, it isn't clear whether C2 (and thus C3)
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
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.
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>
76 #include "blk-mq-tag.h"
78 /* FLUSH/FUA sequences */
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),
85 REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
89 * If flush has been pending longer than the following timeout,
90 * it's issued even if flush_data requests are still in flight.
92 FLUSH_PENDING_TIMEOUT = 5 * HZ,
95 static bool blk_kick_flush(struct request_queue *q,
96 struct blk_flush_queue *fq);
98 static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
100 unsigned int policy = 0;
102 if (blk_rq_sectors(rq))
103 policy |= REQ_FSEQ_DATA;
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;
115 static unsigned int blk_flush_cur_seq(struct request *rq)
117 return 1 << ffz(rq->flush.seq);
120 static void blk_flush_restore_request(struct request *rq)
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.
127 rq->bio = rq->biotail;
129 /* make @rq a normal request */
130 rq->cmd_flags &= ~REQ_FLUSH_SEQ;
131 rq->end_io = rq->flush.saved_end_io;
134 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
137 struct request_queue *q = rq->q;
139 blk_mq_add_to_requeue_list(rq, add_front);
140 blk_mq_kick_requeue_list(q);
144 list_add(&rq->queuelist, &rq->q->queue_head);
146 list_add_tail(&rq->queuelist, &rq->q->queue_head);
152 * blk_flush_complete_seq - complete flush sequence
153 * @rq: FLUSH/FUA request being sequenced
155 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
156 * @error: whether an error occurred
158 * @rq just completed @seq part of its flush sequence, record the
159 * completion and trigger the next step.
162 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
165 * %true if requests were added to the dispatch queue, %false otherwise.
167 static bool blk_flush_complete_seq(struct request *rq,
168 struct blk_flush_queue *fq,
169 unsigned int seq, int error)
171 struct request_queue *q = rq->q;
172 struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
173 bool queued = false, kicked;
175 BUG_ON(rq->flush.seq & seq);
176 rq->flush.seq |= seq;
179 seq = blk_flush_cur_seq(rq);
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);
193 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
194 queued = blk_flush_queue_rq(rq, true);
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.
204 BUG_ON(!list_empty(&rq->queuelist));
205 list_del_init(&rq->flush.list);
206 blk_flush_restore_request(rq);
208 blk_mq_end_request(rq, error);
210 __blk_end_request_all(rq, error);
217 kicked = blk_kick_flush(q, fq);
218 return kicked | queued;
221 static void flush_end_io(struct request *flush_rq, int error)
223 struct request_queue *q = flush_rq->q;
224 struct list_head *running;
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);
231 struct blk_mq_hw_ctx *hctx;
233 /* release the tag's ownership to the req cloned from */
234 spin_lock_irqsave(&fq->mq_flush_lock, flags);
235 hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
236 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
240 running = &fq->flush_queue[fq->flush_running_idx];
241 BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
243 /* account completion of the flush request */
244 fq->flush_running_idx ^= 1;
247 elv_completed_request(q, flush_rq);
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);
253 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
254 queued |= blk_flush_complete_seq(rq, fq, seq, error);
258 * Kick the queue to avoid stall for two cases:
259 * 1. Moving a request silently to empty queue_head may stall the
261 * 2. When flush request is running in non-queueable queue, the
262 * queue is hold. Restart the queue after flush request is finished
264 * This function is called from request completion path and calling
265 * directly into request_fn may confuse the driver. Always use
268 if (queued || fq->flush_queue_delayed) {
270 blk_run_queue_async(q);
272 fq->flush_queue_delayed = 0;
274 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
278 * blk_kick_flush - consider issuing flush request
279 * @q: request_queue being kicked
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.
286 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
289 * %true if flush was issued, %false otherwise.
291 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
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;
298 /* C1 described at the top of this file */
299 if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
303 if (!list_empty(&fq->flush_data_in_flight) &&
305 fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
309 * Issue flush and toggle pending_idx. This makes pending_idx
310 * different from running_idx, which means flush is in flight.
312 fq->flush_pending_idx ^= 1;
314 blk_rq_init(q, flush_rq);
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.
322 struct blk_mq_hw_ctx *hctx;
324 flush_rq->mq_ctx = first_rq->mq_ctx;
325 flush_rq->tag = first_rq->tag;
326 fq->orig_rq = first_rq;
328 hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
329 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
332 flush_rq->cmd_type = REQ_TYPE_FS;
333 req_set_op_attrs(flush_rq, REQ_OP_FLUSH, WRITE_FLUSH | REQ_FLUSH_SEQ);
334 flush_rq->rq_disk = first_rq->rq_disk;
335 flush_rq->end_io = flush_end_io;
337 return blk_flush_queue_rq(flush_rq, false);
340 static void flush_data_end_io(struct request *rq, int error)
342 struct request_queue *q = rq->q;
343 struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
346 * After populating an empty queue, kick it to avoid stall. Read
347 * the comment in flush_end_io().
349 if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
350 blk_run_queue_async(q);
353 static void mq_flush_data_end_io(struct request *rq, int error)
355 struct request_queue *q = rq->q;
356 struct blk_mq_hw_ctx *hctx;
357 struct blk_mq_ctx *ctx = rq->mq_ctx;
359 struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
361 hctx = blk_mq_map_queue(q, ctx->cpu);
364 * After populating an empty queue, kick it to avoid stall. Read
365 * the comment in flush_end_io().
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);
374 * blk_insert_flush - insert a new FLUSH/FUA request
375 * @rq: request to insert
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
383 * spin_lock_irq(q->queue_lock) in !mq case
385 void blk_insert_flush(struct request *rq)
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);
393 * @policy now records what operations need to be done. Adjust
394 * REQ_PREFLUSH and FUA for the driver.
396 rq->cmd_flags &= ~REQ_PREFLUSH;
397 if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
398 rq->cmd_flags &= ~REQ_FUA;
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.
408 blk_mq_end_request(rq, 0);
410 __blk_end_bidi_request(rq, 0, 0, 0);
414 BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
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.
421 if ((policy & REQ_FSEQ_DATA) &&
422 !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
424 blk_mq_insert_request(rq, false, false, true);
426 list_add_tail(&rq->queuelist, &q->queue_head);
431 * @rq should go through flush machinery. Mark it part of flush
432 * sequence and submit for further processing.
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 */
439 rq->end_io = mq_flush_data_end_io;
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);
446 rq->end_io = flush_data_end_io;
448 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
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
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.
463 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
464 sector_t *error_sector)
466 struct request_queue *q;
470 if (bdev->bd_disk == NULL)
473 q = bdev_get_queue(bdev);
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
483 if (!q->make_request_fn)
486 bio = bio_alloc(gfp_mask, 0);
488 bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH);
490 ret = submit_bio_wait(bio);
493 * The driver must store the error location in ->bi_sector, if
494 * it supports it. For non-stacked drivers, this should be
495 * copied from blk_rq_pos(rq).
498 *error_sector = bio->bi_iter.bi_sector;
503 EXPORT_SYMBOL(blkdev_issue_flush);
505 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
506 int node, int cmd_size)
508 struct blk_flush_queue *fq;
509 int rq_sz = sizeof(struct request);
511 fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
516 spin_lock_init(&fq->mq_flush_lock);
517 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
520 fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
524 INIT_LIST_HEAD(&fq->flush_queue[0]);
525 INIT_LIST_HEAD(&fq->flush_queue[1]);
526 INIT_LIST_HEAD(&fq->flush_data_in_flight);
536 void blk_free_flush_queue(struct blk_flush_queue *fq)
538 /* bio based request queue hasn't flush queue */