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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_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
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_FLUSH 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_FLUSH is
27 * 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 * q->flush_queue[q->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
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>
75 /* FLUSH/FUA sequences */
77 REQ_FSEQ_PREFLUSH
= (1 << 0), /* pre-flushing in progress */
78 REQ_FSEQ_DATA
= (1 << 1), /* data write in progress */
79 REQ_FSEQ_POSTFLUSH
= (1 << 2), /* post-flushing in progress */
80 REQ_FSEQ_DONE
= (1 << 3),
82 REQ_FSEQ_ACTIONS
= REQ_FSEQ_PREFLUSH
| REQ_FSEQ_DATA
|
86 * If flush has been pending longer than the following timeout,
87 * it's issued even if flush_data requests are still in flight.
89 FLUSH_PENDING_TIMEOUT
= 5 * HZ
,
92 static bool blk_kick_flush(struct request_queue
*q
);
94 static unsigned int blk_flush_policy(unsigned int fflags
, struct request
*rq
)
96 unsigned int policy
= 0;
98 if (blk_rq_sectors(rq
))
99 policy
|= REQ_FSEQ_DATA
;
101 if (fflags
& REQ_FLUSH
) {
102 if (rq
->cmd_flags
& REQ_FLUSH
)
103 policy
|= REQ_FSEQ_PREFLUSH
;
104 if (!(fflags
& REQ_FUA
) && (rq
->cmd_flags
& REQ_FUA
))
105 policy
|= REQ_FSEQ_POSTFLUSH
;
110 static unsigned int blk_flush_cur_seq(struct request
*rq
)
112 return 1 << ffz(rq
->flush
.seq
);
115 static void blk_flush_restore_request(struct request
*rq
)
118 * After flush data completion, @rq->bio is %NULL but we need to
119 * complete the bio again. @rq->biotail is guaranteed to equal the
120 * original @rq->bio. Restore it.
122 rq
->bio
= rq
->biotail
;
124 /* make @rq a normal request */
125 rq
->cmd_flags
&= ~REQ_FLUSH_SEQ
;
126 rq
->end_io
= rq
->flush
.saved_end_io
;
130 * blk_flush_complete_seq - complete flush sequence
131 * @rq: FLUSH/FUA request being sequenced
132 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
133 * @error: whether an error occurred
135 * @rq just completed @seq part of its flush sequence, record the
136 * completion and trigger the next step.
139 * spin_lock_irq(q->queue_lock)
142 * %true if requests were added to the dispatch queue, %false otherwise.
144 static bool blk_flush_complete_seq(struct request
*rq
, unsigned int seq
,
147 struct request_queue
*q
= rq
->q
;
148 struct list_head
*pending
= &q
->flush_queue
[q
->flush_pending_idx
];
151 BUG_ON(rq
->flush
.seq
& seq
);
152 rq
->flush
.seq
|= seq
;
155 seq
= blk_flush_cur_seq(rq
);
160 case REQ_FSEQ_PREFLUSH
:
161 case REQ_FSEQ_POSTFLUSH
:
162 /* queue for flush */
163 if (list_empty(pending
))
164 q
->flush_pending_since
= jiffies
;
165 list_move_tail(&rq
->flush
.list
, pending
);
169 list_move_tail(&rq
->flush
.list
, &q
->flush_data_in_flight
);
170 list_add(&rq
->queuelist
, &q
->queue_head
);
176 * @rq was previously adjusted by blk_flush_issue() for
177 * flush sequencing and may already have gone through the
178 * flush data request completion path. Restore @rq for
179 * normal completion and end it.
181 BUG_ON(!list_empty(&rq
->queuelist
));
182 list_del_init(&rq
->flush
.list
);
183 blk_flush_restore_request(rq
);
184 __blk_end_request_all(rq
, error
);
191 return blk_kick_flush(q
) | queued
;
194 static void flush_end_io(struct request
*flush_rq
, int error
)
196 struct request_queue
*q
= flush_rq
->q
;
197 struct list_head
*running
= &q
->flush_queue
[q
->flush_running_idx
];
199 struct request
*rq
, *n
;
201 BUG_ON(q
->flush_pending_idx
== q
->flush_running_idx
);
203 /* account completion of the flush request */
204 q
->flush_running_idx
^= 1;
205 elv_completed_request(q
, flush_rq
);
207 /* and push the waiting requests to the next stage */
208 list_for_each_entry_safe(rq
, n
, running
, flush
.list
) {
209 unsigned int seq
= blk_flush_cur_seq(rq
);
211 BUG_ON(seq
!= REQ_FSEQ_PREFLUSH
&& seq
!= REQ_FSEQ_POSTFLUSH
);
212 queued
|= blk_flush_complete_seq(rq
, seq
, error
);
216 * Kick the queue to avoid stall for two cases:
217 * 1. Moving a request silently to empty queue_head may stall the
219 * 2. When flush request is running in non-queueable queue, the
220 * queue is hold. Restart the queue after flush request is finished
222 * This function is called from request completion path and calling
223 * directly into request_fn may confuse the driver. Always use
226 if (queued
|| q
->flush_queue_delayed
)
227 blk_run_queue_async(q
);
228 q
->flush_queue_delayed
= 0;
232 * blk_kick_flush - consider issuing flush request
233 * @q: request_queue being kicked
235 * Flush related states of @q have changed, consider issuing flush request.
236 * Please read the comment at the top of this file for more info.
239 * spin_lock_irq(q->queue_lock)
242 * %true if flush was issued, %false otherwise.
244 static bool blk_kick_flush(struct request_queue
*q
)
246 struct list_head
*pending
= &q
->flush_queue
[q
->flush_pending_idx
];
247 struct request
*first_rq
=
248 list_first_entry(pending
, struct request
, flush
.list
);
250 /* C1 described at the top of this file */
251 if (q
->flush_pending_idx
!= q
->flush_running_idx
|| list_empty(pending
))
255 if (!list_empty(&q
->flush_data_in_flight
) &&
257 q
->flush_pending_since
+ FLUSH_PENDING_TIMEOUT
))
261 * Issue flush and toggle pending_idx. This makes pending_idx
262 * different from running_idx, which means flush is in flight.
264 blk_rq_init(q
, &q
->flush_rq
);
265 q
->flush_rq
.cmd_type
= REQ_TYPE_FS
;
266 q
->flush_rq
.cmd_flags
= WRITE_FLUSH
| REQ_FLUSH_SEQ
;
267 q
->flush_rq
.rq_disk
= first_rq
->rq_disk
;
268 q
->flush_rq
.end_io
= flush_end_io
;
270 q
->flush_pending_idx
^= 1;
271 list_add_tail(&q
->flush_rq
.queuelist
, &q
->queue_head
);
275 static void flush_data_end_io(struct request
*rq
, int error
)
277 struct request_queue
*q
= rq
->q
;
280 * After populating an empty queue, kick it to avoid stall. Read
281 * the comment in flush_end_io().
283 if (blk_flush_complete_seq(rq
, REQ_FSEQ_DATA
, error
))
284 blk_run_queue_async(q
);
288 * blk_insert_flush - insert a new FLUSH/FUA request
289 * @rq: request to insert
291 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
292 * @rq is being submitted. Analyze what needs to be done and put it on the
296 * spin_lock_irq(q->queue_lock)
298 void blk_insert_flush(struct request
*rq
)
300 struct request_queue
*q
= rq
->q
;
301 unsigned int fflags
= q
->flush_flags
; /* may change, cache */
302 unsigned int policy
= blk_flush_policy(fflags
, rq
);
305 * @policy now records what operations need to be done. Adjust
306 * REQ_FLUSH and FUA for the driver.
308 rq
->cmd_flags
&= ~REQ_FLUSH
;
309 if (!(fflags
& REQ_FUA
))
310 rq
->cmd_flags
&= ~REQ_FUA
;
313 * An empty flush handed down from a stacking driver may
314 * translate into nothing if the underlying device does not
315 * advertise a write-back cache. In this case, simply
316 * complete the request.
319 __blk_end_bidi_request(rq
, 0, 0, 0);
323 BUG_ON(rq
->bio
!= rq
->biotail
); /*assumes zero or single bio rq */
326 * If there's data but flush is not necessary, the request can be
327 * processed directly without going through flush machinery. Queue
328 * for normal execution.
330 if ((policy
& REQ_FSEQ_DATA
) &&
331 !(policy
& (REQ_FSEQ_PREFLUSH
| REQ_FSEQ_POSTFLUSH
))) {
332 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
337 * @rq should go through flush machinery. Mark it part of flush
338 * sequence and submit for further processing.
340 memset(&rq
->flush
, 0, sizeof(rq
->flush
));
341 INIT_LIST_HEAD(&rq
->flush
.list
);
342 rq
->cmd_flags
|= REQ_FLUSH_SEQ
;
343 rq
->flush
.saved_end_io
= rq
->end_io
; /* Usually NULL */
344 rq
->end_io
= flush_data_end_io
;
346 blk_flush_complete_seq(rq
, REQ_FSEQ_ACTIONS
& ~policy
, 0);
350 * blk_abort_flushes - @q is being aborted, abort flush requests
351 * @q: request_queue being aborted
353 * To be called from elv_abort_queue(). @q is being aborted. Prepare all
354 * FLUSH/FUA requests for abortion.
357 * spin_lock_irq(q->queue_lock)
359 void blk_abort_flushes(struct request_queue
*q
)
361 struct request
*rq
, *n
;
365 * Requests in flight for data are already owned by the dispatch
366 * queue or the device driver. Just restore for normal completion.
368 list_for_each_entry_safe(rq
, n
, &q
->flush_data_in_flight
, flush
.list
) {
369 list_del_init(&rq
->flush
.list
);
370 blk_flush_restore_request(rq
);
374 * We need to give away requests on flush queues. Restore for
375 * normal completion and put them on the dispatch queue.
377 for (i
= 0; i
< ARRAY_SIZE(q
->flush_queue
); i
++) {
378 list_for_each_entry_safe(rq
, n
, &q
->flush_queue
[i
],
380 list_del_init(&rq
->flush
.list
);
381 blk_flush_restore_request(rq
);
382 list_add_tail(&rq
->queuelist
, &q
->queue_head
);
387 static void bio_end_flush(struct bio
*bio
, int err
)
390 clear_bit(BIO_UPTODATE
, &bio
->bi_flags
);
392 complete(bio
->bi_private
);
397 * blkdev_issue_flush - queue a flush
398 * @bdev: blockdev to issue flush for
399 * @gfp_mask: memory allocation flags (for bio_alloc)
400 * @error_sector: error sector
403 * Issue a flush for the block device in question. Caller can supply
404 * room for storing the error offset in case of a flush error, if they
405 * wish to. If WAIT flag is not passed then caller may check only what
406 * request was pushed in some internal queue for later handling.
408 int blkdev_issue_flush(struct block_device
*bdev
, gfp_t gfp_mask
,
409 sector_t
*error_sector
)
411 DECLARE_COMPLETION_ONSTACK(wait
);
412 struct request_queue
*q
;
416 if (bdev
->bd_disk
== NULL
)
419 q
= bdev_get_queue(bdev
);
424 * some block devices may not have their queue correctly set up here
425 * (e.g. loop device without a backing file) and so issuing a flush
426 * here will panic. Ensure there is a request function before issuing
429 if (!q
->make_request_fn
)
432 bio
= bio_alloc(gfp_mask
, 0);
433 bio
->bi_end_io
= bio_end_flush
;
435 bio
->bi_private
= &wait
;
438 submit_bio(WRITE_FLUSH
, bio
);
439 wait_for_completion(&wait
);
442 * The driver must store the error location in ->bi_sector, if
443 * it supports it. For non-stacked drivers, this should be
444 * copied from blk_rq_pos(rq).
447 *error_sector
= bio
->bi_sector
;
449 if (!bio_flagged(bio
, BIO_UPTODATE
))
455 EXPORT_SYMBOL(blkdev_issue_flush
);