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86db1e29 | 1 | /* |
4fed947c | 2 | * Functions to sequence FLUSH and FUA writes. |
ae1b1539 TH |
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 | * 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 | |
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. | |
86db1e29 | 65 | */ |
ae1b1539 | 66 | |
86db1e29 JA |
67 | #include <linux/kernel.h> |
68 | #include <linux/module.h> | |
69 | #include <linux/bio.h> | |
70 | #include <linux/blkdev.h> | |
5a0e3ad6 | 71 | #include <linux/gfp.h> |
86db1e29 JA |
72 | |
73 | #include "blk.h" | |
74 | ||
4fed947c TH |
75 | /* FLUSH/FUA sequences */ |
76 | enum { | |
ae1b1539 TH |
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), | |
81 | ||
82 | REQ_FSEQ_ACTIONS = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA | | |
83 | REQ_FSEQ_POSTFLUSH, | |
84 | ||
85 | /* | |
86 | * If flush has been pending longer than the following timeout, | |
87 | * it's issued even if flush_data requests are still in flight. | |
88 | */ | |
89 | FLUSH_PENDING_TIMEOUT = 5 * HZ, | |
4fed947c TH |
90 | }; |
91 | ||
ae1b1539 | 92 | static bool blk_kick_flush(struct request_queue *q); |
28e7d184 | 93 | |
ae1b1539 | 94 | static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq) |
86db1e29 | 95 | { |
ae1b1539 | 96 | unsigned int policy = 0; |
86db1e29 | 97 | |
ae1b1539 TH |
98 | if (fflags & REQ_FLUSH) { |
99 | if (rq->cmd_flags & REQ_FLUSH) | |
100 | policy |= REQ_FSEQ_PREFLUSH; | |
101 | if (blk_rq_sectors(rq)) | |
102 | policy |= REQ_FSEQ_DATA; | |
103 | if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA)) | |
104 | policy |= REQ_FSEQ_POSTFLUSH; | |
28e7d184 | 105 | } |
ae1b1539 | 106 | return policy; |
86db1e29 JA |
107 | } |
108 | ||
ae1b1539 | 109 | static unsigned int blk_flush_cur_seq(struct request *rq) |
47f70d5a | 110 | { |
ae1b1539 TH |
111 | return 1 << ffz(rq->flush.seq); |
112 | } | |
47f70d5a | 113 | |
ae1b1539 TH |
114 | static void blk_flush_restore_request(struct request *rq) |
115 | { | |
47f70d5a | 116 | /* |
ae1b1539 TH |
117 | * After flush data completion, @rq->bio is %NULL but we need to |
118 | * complete the bio again. @rq->biotail is guaranteed to equal the | |
119 | * original @rq->bio. Restore it. | |
47f70d5a | 120 | */ |
ae1b1539 TH |
121 | rq->bio = rq->biotail; |
122 | ||
123 | /* make @rq a normal request */ | |
124 | rq->cmd_flags &= ~REQ_FLUSH_SEQ; | |
125 | rq->end_io = NULL; | |
47f70d5a TH |
126 | } |
127 | ||
ae1b1539 TH |
128 | /** |
129 | * blk_flush_complete_seq - complete flush sequence | |
130 | * @rq: FLUSH/FUA request being sequenced | |
131 | * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero) | |
132 | * @error: whether an error occurred | |
133 | * | |
134 | * @rq just completed @seq part of its flush sequence, record the | |
135 | * completion and trigger the next step. | |
136 | * | |
137 | * CONTEXT: | |
138 | * spin_lock_irq(q->queue_lock) | |
139 | * | |
140 | * RETURNS: | |
141 | * %true if requests were added to the dispatch queue, %false otherwise. | |
142 | */ | |
143 | static bool blk_flush_complete_seq(struct request *rq, unsigned int seq, | |
144 | int error) | |
86db1e29 | 145 | { |
ae1b1539 TH |
146 | struct request_queue *q = rq->q; |
147 | struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; | |
148 | bool queued = false; | |
149 | ||
150 | BUG_ON(rq->flush.seq & seq); | |
151 | rq->flush.seq |= seq; | |
152 | ||
153 | if (likely(!error)) | |
154 | seq = blk_flush_cur_seq(rq); | |
155 | else | |
156 | seq = REQ_FSEQ_DONE; | |
157 | ||
158 | switch (seq) { | |
159 | case REQ_FSEQ_PREFLUSH: | |
160 | case REQ_FSEQ_POSTFLUSH: | |
161 | /* queue for flush */ | |
162 | if (list_empty(pending)) | |
163 | q->flush_pending_since = jiffies; | |
164 | list_move_tail(&rq->flush.list, pending); | |
165 | break; | |
166 | ||
167 | case REQ_FSEQ_DATA: | |
168 | list_move_tail(&rq->flush.list, &q->flush_data_in_flight); | |
169 | list_add(&rq->queuelist, &q->queue_head); | |
170 | queued = true; | |
171 | break; | |
172 | ||
173 | case REQ_FSEQ_DONE: | |
174 | /* | |
175 | * @rq was previously adjusted by blk_flush_issue() for | |
176 | * flush sequencing and may already have gone through the | |
177 | * flush data request completion path. Restore @rq for | |
178 | * normal completion and end it. | |
179 | */ | |
180 | BUG_ON(!list_empty(&rq->queuelist)); | |
181 | list_del_init(&rq->flush.list); | |
182 | blk_flush_restore_request(rq); | |
183 | __blk_end_request_all(rq, error); | |
184 | break; | |
185 | ||
186 | default: | |
187 | BUG(); | |
188 | } | |
189 | ||
190 | return blk_kick_flush(q) | queued; | |
86db1e29 JA |
191 | } |
192 | ||
ae1b1539 | 193 | static void flush_end_io(struct request *flush_rq, int error) |
86db1e29 | 194 | { |
ae1b1539 TH |
195 | struct request_queue *q = flush_rq->q; |
196 | struct list_head *running = &q->flush_queue[q->flush_running_idx]; | |
ae1b1539 TH |
197 | bool queued = false; |
198 | struct request *rq, *n; | |
199 | ||
200 | BUG_ON(q->flush_pending_idx == q->flush_running_idx); | |
201 | ||
202 | /* account completion of the flush request */ | |
203 | q->flush_running_idx ^= 1; | |
204 | elv_completed_request(q, flush_rq); | |
205 | ||
206 | /* and push the waiting requests to the next stage */ | |
207 | list_for_each_entry_safe(rq, n, running, flush.list) { | |
208 | unsigned int seq = blk_flush_cur_seq(rq); | |
209 | ||
210 | BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH); | |
211 | queued |= blk_flush_complete_seq(rq, seq, error); | |
212 | } | |
213 | ||
47f70d5a TH |
214 | /* |
215 | * Moving a request silently to empty queue_head may stall the | |
255bb490 TH |
216 | * queue. Kick the queue in those cases. This function is called |
217 | * from request completion path and calling directly into | |
218 | * request_fn may confuse the driver. Always use kblockd. | |
47f70d5a | 219 | */ |
7eaceacc | 220 | if (queued) |
255bb490 | 221 | __blk_run_queue(q, true); |
86db1e29 JA |
222 | } |
223 | ||
ae1b1539 TH |
224 | /** |
225 | * blk_kick_flush - consider issuing flush request | |
226 | * @q: request_queue being kicked | |
227 | * | |
228 | * Flush related states of @q have changed, consider issuing flush request. | |
229 | * Please read the comment at the top of this file for more info. | |
230 | * | |
231 | * CONTEXT: | |
232 | * spin_lock_irq(q->queue_lock) | |
233 | * | |
234 | * RETURNS: | |
235 | * %true if flush was issued, %false otherwise. | |
236 | */ | |
237 | static bool blk_kick_flush(struct request_queue *q) | |
86db1e29 | 238 | { |
ae1b1539 TH |
239 | struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; |
240 | struct request *first_rq = | |
241 | list_first_entry(pending, struct request, flush.list); | |
242 | ||
243 | /* C1 described at the top of this file */ | |
244 | if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending)) | |
245 | return false; | |
246 | ||
247 | /* C2 and C3 */ | |
248 | if (!list_empty(&q->flush_data_in_flight) && | |
249 | time_before(jiffies, | |
250 | q->flush_pending_since + FLUSH_PENDING_TIMEOUT)) | |
251 | return false; | |
252 | ||
253 | /* | |
254 | * Issue flush and toggle pending_idx. This makes pending_idx | |
255 | * different from running_idx, which means flush is in flight. | |
256 | */ | |
257 | blk_rq_init(q, &q->flush_rq); | |
258 | q->flush_rq.cmd_type = REQ_TYPE_FS; | |
259 | q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ; | |
260 | q->flush_rq.rq_disk = first_rq->rq_disk; | |
261 | q->flush_rq.end_io = flush_end_io; | |
262 | ||
263 | q->flush_pending_idx ^= 1; | |
e83a46bb | 264 | elv_insert(q, &q->flush_rq, ELEVATOR_INSERT_REQUEUE); |
ae1b1539 | 265 | return true; |
86db1e29 JA |
266 | } |
267 | ||
ae1b1539 | 268 | static void flush_data_end_io(struct request *rq, int error) |
86db1e29 | 269 | { |
ae1b1539 | 270 | struct request_queue *q = rq->q; |
ae1b1539 | 271 | |
e83a46bb TH |
272 | /* |
273 | * After populating an empty queue, kick it to avoid stall. Read | |
274 | * the comment in flush_end_io(). | |
275 | */ | |
73c10101 | 276 | if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error)) |
e83a46bb | 277 | __blk_run_queue(q, true); |
86db1e29 JA |
278 | } |
279 | ||
ae1b1539 TH |
280 | /** |
281 | * blk_insert_flush - insert a new FLUSH/FUA request | |
282 | * @rq: request to insert | |
283 | * | |
284 | * To be called from elv_insert() for %ELEVATOR_INSERT_FLUSH insertions. | |
285 | * @rq is being submitted. Analyze what needs to be done and put it on the | |
286 | * right queue. | |
287 | * | |
288 | * CONTEXT: | |
289 | * spin_lock_irq(q->queue_lock) | |
290 | */ | |
291 | void blk_insert_flush(struct request *rq) | |
86db1e29 | 292 | { |
ae1b1539 TH |
293 | struct request_queue *q = rq->q; |
294 | unsigned int fflags = q->flush_flags; /* may change, cache */ | |
295 | unsigned int policy = blk_flush_policy(fflags, rq); | |
86db1e29 | 296 | |
ae1b1539 TH |
297 | BUG_ON(rq->end_io); |
298 | BUG_ON(!rq->bio || rq->bio != rq->biotail); | |
cde4c406 | 299 | |
ae1b1539 TH |
300 | /* |
301 | * @policy now records what operations need to be done. Adjust | |
302 | * REQ_FLUSH and FUA for the driver. | |
303 | */ | |
304 | rq->cmd_flags &= ~REQ_FLUSH; | |
305 | if (!(fflags & REQ_FUA)) | |
306 | rq->cmd_flags &= ~REQ_FUA; | |
307 | ||
308 | /* | |
309 | * If there's data but flush is not necessary, the request can be | |
310 | * processed directly without going through flush machinery. Queue | |
311 | * for normal execution. | |
312 | */ | |
313 | if ((policy & REQ_FSEQ_DATA) && | |
314 | !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) { | |
315 | list_add(&rq->queuelist, &q->queue_head); | |
316 | return; | |
28e7d184 | 317 | } |
cde4c406 | 318 | |
ae1b1539 TH |
319 | /* |
320 | * @rq should go through flush machinery. Mark it part of flush | |
321 | * sequence and submit for further processing. | |
322 | */ | |
323 | memset(&rq->flush, 0, sizeof(rq->flush)); | |
324 | INIT_LIST_HEAD(&rq->flush.list); | |
414b4ff5 | 325 | rq->cmd_flags |= REQ_FLUSH_SEQ; |
ae1b1539 TH |
326 | rq->end_io = flush_data_end_io; |
327 | ||
328 | blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0); | |
86db1e29 JA |
329 | } |
330 | ||
ae1b1539 TH |
331 | /** |
332 | * blk_abort_flushes - @q is being aborted, abort flush requests | |
333 | * @q: request_queue being aborted | |
334 | * | |
335 | * To be called from elv_abort_queue(). @q is being aborted. Prepare all | |
336 | * FLUSH/FUA requests for abortion. | |
337 | * | |
338 | * CONTEXT: | |
339 | * spin_lock_irq(q->queue_lock) | |
340 | */ | |
341 | void blk_abort_flushes(struct request_queue *q) | |
86db1e29 | 342 | { |
ae1b1539 TH |
343 | struct request *rq, *n; |
344 | int i; | |
28e7d184 | 345 | |
4fed947c | 346 | /* |
ae1b1539 TH |
347 | * Requests in flight for data are already owned by the dispatch |
348 | * queue or the device driver. Just restore for normal completion. | |
4fed947c | 349 | */ |
ae1b1539 TH |
350 | list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) { |
351 | list_del_init(&rq->flush.list); | |
352 | blk_flush_restore_request(rq); | |
4fed947c | 353 | } |
28e7d184 | 354 | |
4fed947c | 355 | /* |
ae1b1539 TH |
356 | * We need to give away requests on flush queues. Restore for |
357 | * normal completion and put them on the dispatch queue. | |
4fed947c | 358 | */ |
ae1b1539 TH |
359 | for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) { |
360 | list_for_each_entry_safe(rq, n, &q->flush_queue[i], | |
361 | flush.list) { | |
362 | list_del_init(&rq->flush.list); | |
363 | blk_flush_restore_request(rq); | |
364 | list_add_tail(&rq->queuelist, &q->queue_head); | |
365 | } | |
28e7d184 | 366 | } |
86db1e29 JA |
367 | } |
368 | ||
d391a2dd | 369 | static void bio_end_flush(struct bio *bio, int err) |
86db1e29 | 370 | { |
d391a2dd | 371 | if (err) |
86db1e29 | 372 | clear_bit(BIO_UPTODATE, &bio->bi_flags); |
f17e232e DM |
373 | if (bio->bi_private) |
374 | complete(bio->bi_private); | |
375 | bio_put(bio); | |
86db1e29 JA |
376 | } |
377 | ||
378 | /** | |
379 | * blkdev_issue_flush - queue a flush | |
380 | * @bdev: blockdev to issue flush for | |
fbd9b09a | 381 | * @gfp_mask: memory allocation flags (for bio_alloc) |
86db1e29 JA |
382 | * @error_sector: error sector |
383 | * | |
384 | * Description: | |
385 | * Issue a flush for the block device in question. Caller can supply | |
386 | * room for storing the error offset in case of a flush error, if they | |
f17e232e DM |
387 | * wish to. If WAIT flag is not passed then caller may check only what |
388 | * request was pushed in some internal queue for later handling. | |
86db1e29 | 389 | */ |
fbd9b09a | 390 | int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, |
dd3932ed | 391 | sector_t *error_sector) |
86db1e29 JA |
392 | { |
393 | DECLARE_COMPLETION_ONSTACK(wait); | |
394 | struct request_queue *q; | |
395 | struct bio *bio; | |
fbd9b09a | 396 | int ret = 0; |
86db1e29 JA |
397 | |
398 | if (bdev->bd_disk == NULL) | |
399 | return -ENXIO; | |
400 | ||
401 | q = bdev_get_queue(bdev); | |
402 | if (!q) | |
403 | return -ENXIO; | |
404 | ||
f10d9f61 DC |
405 | /* |
406 | * some block devices may not have their queue correctly set up here | |
407 | * (e.g. loop device without a backing file) and so issuing a flush | |
408 | * here will panic. Ensure there is a request function before issuing | |
d391a2dd | 409 | * the flush. |
f10d9f61 DC |
410 | */ |
411 | if (!q->make_request_fn) | |
412 | return -ENXIO; | |
413 | ||
fbd9b09a | 414 | bio = bio_alloc(gfp_mask, 0); |
d391a2dd | 415 | bio->bi_end_io = bio_end_flush; |
86db1e29 | 416 | bio->bi_bdev = bdev; |
dd3932ed | 417 | bio->bi_private = &wait; |
86db1e29 | 418 | |
f17e232e | 419 | bio_get(bio); |
d391a2dd | 420 | submit_bio(WRITE_FLUSH, bio); |
dd3932ed CH |
421 | wait_for_completion(&wait); |
422 | ||
423 | /* | |
424 | * The driver must store the error location in ->bi_sector, if | |
425 | * it supports it. For non-stacked drivers, this should be | |
426 | * copied from blk_rq_pos(rq). | |
427 | */ | |
428 | if (error_sector) | |
429 | *error_sector = bio->bi_sector; | |
86db1e29 | 430 | |
d391a2dd | 431 | if (!bio_flagged(bio, BIO_UPTODATE)) |
86db1e29 JA |
432 | ret = -EIO; |
433 | ||
434 | bio_put(bio); | |
435 | return ret; | |
436 | } | |
86db1e29 | 437 | EXPORT_SYMBOL(blkdev_issue_flush); |