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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 | * 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. |
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 | |
73 | #include "blk.h" |
74 | |
75 | /* FLUSH/FUA sequences */ |
76 | enum { |
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, |
90 | }; |
91 | |
92 | static bool blk_kick_flush(struct request_queue *q); |
93 | |
94 | static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq) |
95 | { |
96 | unsigned int policy = 0; |
97 | |
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; |
105 | } |
106 | return policy; |
107 | } |
108 | |
109 | static unsigned int blk_flush_cur_seq(struct request *rq) |
110 | { |
111 | return 1 << ffz(rq->flush.seq); |
112 | } |
113 | |
114 | static void blk_flush_restore_request(struct request *rq) |
115 | { |
116 | /* |
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. |
120 | */ |
121 | rq->bio = rq->biotail; |
122 | |
123 | /* make @rq a normal request */ |
124 | rq->cmd_flags &= ~REQ_FLUSH_SEQ; |
125 | rq->end_io = NULL; |
126 | } |
127 | |
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) |
145 | { |
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; |
191 | } |
192 | |
193 | static void flush_end_io(struct request *flush_rq, int error) |
194 | { |
195 | struct request_queue *q = flush_rq->q; |
196 | struct list_head *running = &q->flush_queue[q->flush_running_idx]; |
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 | |
214 | /* |
215 | * Kick the queue to avoid stall for two cases: |
216 | * 1. Moving a request silently to empty queue_head may stall the |
217 | * queue. |
218 | * 2. When flush request is running in non-queueable queue, the |
219 | * queue is hold. Restart the queue after flush request is finished |
220 | * to avoid stall. |
221 | * This function is called from request completion path and calling |
222 | * directly into request_fn may confuse the driver. Always use |
223 | * kblockd. |
224 | */ |
225 | if (queued || q->flush_queue_delayed) |
226 | blk_run_queue_async(q); |
227 | q->flush_queue_delayed = 0; |
228 | } |
229 | |
230 | /** |
231 | * blk_kick_flush - consider issuing flush request |
232 | * @q: request_queue being kicked |
233 | * |
234 | * Flush related states of @q have changed, consider issuing flush request. |
235 | * Please read the comment at the top of this file for more info. |
236 | * |
237 | * CONTEXT: |
238 | * spin_lock_irq(q->queue_lock) |
239 | * |
240 | * RETURNS: |
241 | * %true if flush was issued, %false otherwise. |
242 | */ |
243 | static bool blk_kick_flush(struct request_queue *q) |
244 | { |
245 | struct list_head *pending = &q->flush_queue[q->flush_pending_idx]; |
246 | struct request *first_rq = |
247 | list_first_entry(pending, struct request, flush.list); |
248 | |
249 | /* C1 described at the top of this file */ |
250 | if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending)) |
251 | return false; |
252 | |
253 | /* C2 and C3 */ |
254 | if (!list_empty(&q->flush_data_in_flight) && |
255 | time_before(jiffies, |
256 | q->flush_pending_since + FLUSH_PENDING_TIMEOUT)) |
257 | return false; |
258 | |
259 | /* |
260 | * Issue flush and toggle pending_idx. This makes pending_idx |
261 | * different from running_idx, which means flush is in flight. |
262 | */ |
263 | blk_rq_init(q, &q->flush_rq); |
264 | q->flush_rq.cmd_type = REQ_TYPE_FS; |
265 | q->flush_rq.cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ; |
266 | q->flush_rq.rq_disk = first_rq->rq_disk; |
267 | q->flush_rq.end_io = flush_end_io; |
268 | |
269 | q->flush_pending_idx ^= 1; |
270 | list_add_tail(&q->flush_rq.queuelist, &q->queue_head); |
271 | return true; |
272 | } |
273 | |
274 | static void flush_data_end_io(struct request *rq, int error) |
275 | { |
276 | struct request_queue *q = rq->q; |
277 | |
278 | /* |
279 | * After populating an empty queue, kick it to avoid stall. Read |
280 | * the comment in flush_end_io(). |
281 | */ |
282 | if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error)) |
283 | blk_run_queue_async(q); |
284 | } |
285 | |
286 | /** |
287 | * blk_insert_flush - insert a new FLUSH/FUA request |
288 | * @rq: request to insert |
289 | * |
290 | * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions. |
291 | * @rq is being submitted. Analyze what needs to be done and put it on the |
292 | * right queue. |
293 | * |
294 | * CONTEXT: |
295 | * spin_lock_irq(q->queue_lock) |
296 | */ |
297 | void blk_insert_flush(struct request *rq) |
298 | { |
299 | struct request_queue *q = rq->q; |
300 | unsigned int fflags = q->flush_flags; /* may change, cache */ |
301 | unsigned int policy = blk_flush_policy(fflags, rq); |
302 | |
303 | BUG_ON(rq->end_io); |
304 | BUG_ON(!rq->bio || rq->bio != rq->biotail); |
305 | |
306 | /* |
307 | * @policy now records what operations need to be done. Adjust |
308 | * REQ_FLUSH and FUA for the driver. |
309 | */ |
310 | rq->cmd_flags &= ~REQ_FLUSH; |
311 | if (!(fflags & REQ_FUA)) |
312 | rq->cmd_flags &= ~REQ_FUA; |
313 | |
314 | /* |
315 | * If there's data but flush is not necessary, the request can be |
316 | * processed directly without going through flush machinery. Queue |
317 | * for normal execution. |
318 | */ |
319 | if ((policy & REQ_FSEQ_DATA) && |
320 | !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) { |
321 | list_add_tail(&rq->queuelist, &q->queue_head); |
322 | return; |
323 | } |
324 | |
325 | /* |
326 | * @rq should go through flush machinery. Mark it part of flush |
327 | * sequence and submit for further processing. |
328 | */ |
329 | memset(&rq->flush, 0, sizeof(rq->flush)); |
330 | INIT_LIST_HEAD(&rq->flush.list); |
331 | rq->cmd_flags |= REQ_FLUSH_SEQ; |
332 | rq->end_io = flush_data_end_io; |
333 | |
334 | blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0); |
335 | } |
336 | |
337 | /** |
338 | * blk_abort_flushes - @q is being aborted, abort flush requests |
339 | * @q: request_queue being aborted |
340 | * |
341 | * To be called from elv_abort_queue(). @q is being aborted. Prepare all |
342 | * FLUSH/FUA requests for abortion. |
343 | * |
344 | * CONTEXT: |
345 | * spin_lock_irq(q->queue_lock) |
346 | */ |
347 | void blk_abort_flushes(struct request_queue *q) |
348 | { |
349 | struct request *rq, *n; |
350 | int i; |
351 | |
352 | /* |
353 | * Requests in flight for data are already owned by the dispatch |
354 | * queue or the device driver. Just restore for normal completion. |
355 | */ |
356 | list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) { |
357 | list_del_init(&rq->flush.list); |
358 | blk_flush_restore_request(rq); |
359 | } |
360 | |
361 | /* |
362 | * We need to give away requests on flush queues. Restore for |
363 | * normal completion and put them on the dispatch queue. |
364 | */ |
365 | for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) { |
366 | list_for_each_entry_safe(rq, n, &q->flush_queue[i], |
367 | flush.list) { |
368 | list_del_init(&rq->flush.list); |
369 | blk_flush_restore_request(rq); |
370 | list_add_tail(&rq->queuelist, &q->queue_head); |
371 | } |
372 | } |
373 | } |
374 | |
375 | static void bio_end_flush(struct bio *bio, int err) |
376 | { |
377 | if (err) |
378 | clear_bit(BIO_UPTODATE, &bio->bi_flags); |
379 | if (bio->bi_private) |
380 | complete(bio->bi_private); |
381 | bio_put(bio); |
382 | } |
383 | |
384 | /** |
385 | * blkdev_issue_flush - queue a flush |
386 | * @bdev: blockdev to issue flush for |
387 | * @gfp_mask: memory allocation flags (for bio_alloc) |
388 | * @error_sector: error sector |
389 | * |
390 | * Description: |
391 | * Issue a flush for the block device in question. Caller can supply |
392 | * room for storing the error offset in case of a flush error, if they |
393 | * wish to. If WAIT flag is not passed then caller may check only what |
394 | * request was pushed in some internal queue for later handling. |
395 | */ |
396 | int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask, |
397 | sector_t *error_sector) |
398 | { |
399 | DECLARE_COMPLETION_ONSTACK(wait); |
400 | struct request_queue *q; |
401 | struct bio *bio; |
402 | int ret = 0; |
403 | |
404 | if (bdev->bd_disk == NULL) |
405 | return -ENXIO; |
406 | |
407 | q = bdev_get_queue(bdev); |
408 | if (!q) |
409 | return -ENXIO; |
410 | |
411 | /* |
412 | * some block devices may not have their queue correctly set up here |
413 | * (e.g. loop device without a backing file) and so issuing a flush |
414 | * here will panic. Ensure there is a request function before issuing |
415 | * the flush. |
416 | */ |
417 | if (!q->make_request_fn) |
418 | return -ENXIO; |
419 | |
420 | bio = bio_alloc(gfp_mask, 0); |
421 | bio->bi_end_io = bio_end_flush; |
422 | bio->bi_bdev = bdev; |
423 | bio->bi_private = &wait; |
424 | |
425 | bio_get(bio); |
426 | submit_bio(WRITE_FLUSH, bio); |
427 | wait_for_completion(&wait); |
428 | |
429 | /* |
430 | * The driver must store the error location in ->bi_sector, if |
431 | * it supports it. For non-stacked drivers, this should be |
432 | * copied from blk_rq_pos(rq). |
433 | */ |
434 | if (error_sector) |
435 | *error_sector = bio->bi_sector; |
436 | |
437 | if (!bio_flagged(bio, BIO_UPTODATE)) |
438 | ret = -EIO; |
439 | |
440 | bio_put(bio); |
441 | return ret; |
442 | } |
443 | EXPORT_SYMBOL(blkdev_issue_flush); |
444 |
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