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Linux/block/blk-flush.c

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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 #include <linux/blk-mq.h>
 73 
 74 #include "blk.h"
 75 #include "blk-mq.h"
 76 
 77 /* FLUSH/FUA sequences */
 78 enum {
 79         REQ_FSEQ_PREFLUSH       = (1 << 0), /* pre-flushing in progress */
 80         REQ_FSEQ_DATA           = (1 << 1), /* data write in progress */
 81         REQ_FSEQ_POSTFLUSH      = (1 << 2), /* post-flushing in progress */
 82         REQ_FSEQ_DONE           = (1 << 3),
 83 
 84         REQ_FSEQ_ACTIONS        = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
 85                                   REQ_FSEQ_POSTFLUSH,
 86 
 87         /*
 88          * If flush has been pending longer than the following timeout,
 89          * it's issued even if flush_data requests are still in flight.
 90          */
 91         FLUSH_PENDING_TIMEOUT   = 5 * HZ,
 92 };
 93 
 94 static bool blk_kick_flush(struct request_queue *q);
 95 
 96 static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
 97 {
 98         unsigned int policy = 0;
 99 
100         if (blk_rq_sectors(rq))
101                 policy |= REQ_FSEQ_DATA;
102 
103         if (fflags & REQ_FLUSH) {
104                 if (rq->cmd_flags & REQ_FLUSH)
105                         policy |= REQ_FSEQ_PREFLUSH;
106                 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
107                         policy |= REQ_FSEQ_POSTFLUSH;
108         }
109         return policy;
110 }
111 
112 static unsigned int blk_flush_cur_seq(struct request *rq)
113 {
114         return 1 << ffz(rq->flush.seq);
115 }
116 
117 static void blk_flush_restore_request(struct request *rq)
118 {
119         /*
120          * After flush data completion, @rq->bio is %NULL but we need to
121          * complete the bio again.  @rq->biotail is guaranteed to equal the
122          * original @rq->bio.  Restore it.
123          */
124         rq->bio = rq->biotail;
125 
126         /* make @rq a normal request */
127         rq->cmd_flags &= ~REQ_FLUSH_SEQ;
128         rq->end_io = rq->flush.saved_end_io;
129 
130         blk_clear_rq_complete(rq);
131 }
132 
133 static void mq_flush_run(struct work_struct *work)
134 {
135         struct request *rq;
136 
137         rq = container_of(work, struct request, mq_flush_work);
138 
139         memset(&rq->csd, 0, sizeof(rq->csd));
140         blk_mq_insert_request(rq, false, true, false);
141 }
142 
143 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
144 {
145         if (rq->q->mq_ops) {
146                 INIT_WORK(&rq->mq_flush_work, mq_flush_run);
147                 kblockd_schedule_work(rq->q, &rq->mq_flush_work);
148                 return false;
149         } else {
150                 if (add_front)
151                         list_add(&rq->queuelist, &rq->q->queue_head);
152                 else
153                         list_add_tail(&rq->queuelist, &rq->q->queue_head);
154                 return true;
155         }
156 }
157 
158 /**
159  * blk_flush_complete_seq - complete flush sequence
160  * @rq: FLUSH/FUA request being sequenced
161  * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
162  * @error: whether an error occurred
163  *
164  * @rq just completed @seq part of its flush sequence, record the
165  * completion and trigger the next step.
166  *
167  * CONTEXT:
168  * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
169  *
170  * RETURNS:
171  * %true if requests were added to the dispatch queue, %false otherwise.
172  */
173 static bool blk_flush_complete_seq(struct request *rq, unsigned int seq,
174                                    int error)
175 {
176         struct request_queue *q = rq->q;
177         struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
178         bool queued = false, kicked;
179 
180         BUG_ON(rq->flush.seq & seq);
181         rq->flush.seq |= seq;
182 
183         if (likely(!error))
184                 seq = blk_flush_cur_seq(rq);
185         else
186                 seq = REQ_FSEQ_DONE;
187 
188         switch (seq) {
189         case REQ_FSEQ_PREFLUSH:
190         case REQ_FSEQ_POSTFLUSH:
191                 /* queue for flush */
192                 if (list_empty(pending))
193                         q->flush_pending_since = jiffies;
194                 list_move_tail(&rq->flush.list, pending);
195                 break;
196 
197         case REQ_FSEQ_DATA:
198                 list_move_tail(&rq->flush.list, &q->flush_data_in_flight);
199                 queued = blk_flush_queue_rq(rq, true);
200                 break;
201 
202         case REQ_FSEQ_DONE:
203                 /*
204                  * @rq was previously adjusted by blk_flush_issue() for
205                  * flush sequencing and may already have gone through the
206                  * flush data request completion path.  Restore @rq for
207                  * normal completion and end it.
208                  */
209                 BUG_ON(!list_empty(&rq->queuelist));
210                 list_del_init(&rq->flush.list);
211                 blk_flush_restore_request(rq);
212                 if (q->mq_ops)
213                         blk_mq_end_io(rq, error);
214                 else
215                         __blk_end_request_all(rq, error);
216                 break;
217 
218         default:
219                 BUG();
220         }
221 
222         kicked = blk_kick_flush(q);
223         return kicked | queued;
224 }
225 
226 static void flush_end_io(struct request *flush_rq, int error)
227 {
228         struct request_queue *q = flush_rq->q;
229         struct list_head *running;
230         bool queued = false;
231         struct request *rq, *n;
232         unsigned long flags = 0;
233 
234         if (q->mq_ops)
235                 spin_lock_irqsave(&q->mq_flush_lock, flags);
236 
237         running = &q->flush_queue[q->flush_running_idx];
238         BUG_ON(q->flush_pending_idx == q->flush_running_idx);
239 
240         /* account completion of the flush request */
241         q->flush_running_idx ^= 1;
242 
243         if (!q->mq_ops)
244                 elv_completed_request(q, flush_rq);
245 
246         /* and push the waiting requests to the next stage */
247         list_for_each_entry_safe(rq, n, running, flush.list) {
248                 unsigned int seq = blk_flush_cur_seq(rq);
249 
250                 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
251                 queued |= blk_flush_complete_seq(rq, seq, error);
252         }
253 
254         /*
255          * Kick the queue to avoid stall for two cases:
256          * 1. Moving a request silently to empty queue_head may stall the
257          * queue.
258          * 2. When flush request is running in non-queueable queue, the
259          * queue is hold. Restart the queue after flush request is finished
260          * to avoid stall.
261          * This function is called from request completion path and calling
262          * directly into request_fn may confuse the driver.  Always use
263          * kblockd.
264          */
265         if (queued || q->flush_queue_delayed) {
266                 WARN_ON(q->mq_ops);
267                 blk_run_queue_async(q);
268         }
269         q->flush_queue_delayed = 0;
270         if (q->mq_ops)
271                 spin_unlock_irqrestore(&q->mq_flush_lock, flags);
272 }
273 
274 /**
275  * blk_kick_flush - consider issuing flush request
276  * @q: request_queue being kicked
277  *
278  * Flush related states of @q have changed, consider issuing flush request.
279  * Please read the comment at the top of this file for more info.
280  *
281  * CONTEXT:
282  * spin_lock_irq(q->queue_lock or q->mq_flush_lock)
283  *
284  * RETURNS:
285  * %true if flush was issued, %false otherwise.
286  */
287 static bool blk_kick_flush(struct request_queue *q)
288 {
289         struct list_head *pending = &q->flush_queue[q->flush_pending_idx];
290         struct request *first_rq =
291                 list_first_entry(pending, struct request, flush.list);
292 
293         /* C1 described at the top of this file */
294         if (q->flush_pending_idx != q->flush_running_idx || list_empty(pending))
295                 return false;
296 
297         /* C2 and C3 */
298         if (!list_empty(&q->flush_data_in_flight) &&
299             time_before(jiffies,
300                         q->flush_pending_since + FLUSH_PENDING_TIMEOUT))
301                 return false;
302 
303         /*
304          * Issue flush and toggle pending_idx.  This makes pending_idx
305          * different from running_idx, which means flush is in flight.
306          */
307         q->flush_pending_idx ^= 1;
308 
309         if (q->mq_ops) {
310                 struct blk_mq_ctx *ctx = first_rq->mq_ctx;
311                 struct blk_mq_hw_ctx *hctx = q->mq_ops->map_queue(q, ctx->cpu);
312 
313                 blk_mq_rq_init(hctx, q->flush_rq);
314                 q->flush_rq->mq_ctx = ctx;
315 
316                 /*
317                  * Reuse the tag value from the fist waiting request,
318                  * with blk-mq the tag is generated during request
319                  * allocation and drivers can rely on it being inside
320                  * the range they asked for.
321                  */
322                 q->flush_rq->tag = first_rq->tag;
323         } else {
324                 blk_rq_init(q, q->flush_rq);
325         }
326 
327         q->flush_rq->cmd_type = REQ_TYPE_FS;
328         q->flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
329         q->flush_rq->rq_disk = first_rq->rq_disk;
330         q->flush_rq->end_io = flush_end_io;
331 
332         return blk_flush_queue_rq(q->flush_rq, false);
333 }
334 
335 static void flush_data_end_io(struct request *rq, int error)
336 {
337         struct request_queue *q = rq->q;
338 
339         /*
340          * After populating an empty queue, kick it to avoid stall.  Read
341          * the comment in flush_end_io().
342          */
343         if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
344                 blk_run_queue_async(q);
345 }
346 
347 static void mq_flush_data_end_io(struct request *rq, int error)
348 {
349         struct request_queue *q = rq->q;
350         struct blk_mq_hw_ctx *hctx;
351         struct blk_mq_ctx *ctx;
352         unsigned long flags;
353 
354         ctx = rq->mq_ctx;
355         hctx = q->mq_ops->map_queue(q, ctx->cpu);
356 
357         /*
358          * After populating an empty queue, kick it to avoid stall.  Read
359          * the comment in flush_end_io().
360          */
361         spin_lock_irqsave(&q->mq_flush_lock, flags);
362         if (blk_flush_complete_seq(rq, REQ_FSEQ_DATA, error))
363                 blk_mq_run_hw_queue(hctx, true);
364         spin_unlock_irqrestore(&q->mq_flush_lock, flags);
365 }
366 
367 /**
368  * blk_insert_flush - insert a new FLUSH/FUA request
369  * @rq: request to insert
370  *
371  * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
372  * or __blk_mq_run_hw_queue() to dispatch request.
373  * @rq is being submitted.  Analyze what needs to be done and put it on the
374  * right queue.
375  *
376  * CONTEXT:
377  * spin_lock_irq(q->queue_lock) in !mq case
378  */
379 void blk_insert_flush(struct request *rq)
380 {
381         struct request_queue *q = rq->q;
382         unsigned int fflags = q->flush_flags;   /* may change, cache */
383         unsigned int policy = blk_flush_policy(fflags, rq);
384 
385         /*
386          * @policy now records what operations need to be done.  Adjust
387          * REQ_FLUSH and FUA for the driver.
388          */
389         rq->cmd_flags &= ~REQ_FLUSH;
390         if (!(fflags & REQ_FUA))
391                 rq->cmd_flags &= ~REQ_FUA;
392 
393         /*
394          * An empty flush handed down from a stacking driver may
395          * translate into nothing if the underlying device does not
396          * advertise a write-back cache.  In this case, simply
397          * complete the request.
398          */
399         if (!policy) {
400                 if (q->mq_ops)
401                         blk_mq_end_io(rq, 0);
402                 else
403                         __blk_end_bidi_request(rq, 0, 0, 0);
404                 return;
405         }
406 
407         BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
408 
409         /*
410          * If there's data but flush is not necessary, the request can be
411          * processed directly without going through flush machinery.  Queue
412          * for normal execution.
413          */
414         if ((policy & REQ_FSEQ_DATA) &&
415             !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
416                 if (q->mq_ops) {
417                         blk_mq_insert_request(rq, false, false, true);
418                 } else
419                         list_add_tail(&rq->queuelist, &q->queue_head);
420                 return;
421         }
422 
423         /*
424          * @rq should go through flush machinery.  Mark it part of flush
425          * sequence and submit for further processing.
426          */
427         memset(&rq->flush, 0, sizeof(rq->flush));
428         INIT_LIST_HEAD(&rq->flush.list);
429         rq->cmd_flags |= REQ_FLUSH_SEQ;
430         rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
431         if (q->mq_ops) {
432                 rq->end_io = mq_flush_data_end_io;
433 
434                 spin_lock_irq(&q->mq_flush_lock);
435                 blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
436                 spin_unlock_irq(&q->mq_flush_lock);
437                 return;
438         }
439         rq->end_io = flush_data_end_io;
440 
441         blk_flush_complete_seq(rq, REQ_FSEQ_ACTIONS & ~policy, 0);
442 }
443 
444 /**
445  * blk_abort_flushes - @q is being aborted, abort flush requests
446  * @q: request_queue being aborted
447  *
448  * To be called from elv_abort_queue().  @q is being aborted.  Prepare all
449  * FLUSH/FUA requests for abortion.
450  *
451  * CONTEXT:
452  * spin_lock_irq(q->queue_lock)
453  */
454 void blk_abort_flushes(struct request_queue *q)
455 {
456         struct request *rq, *n;
457         int i;
458 
459         /*
460          * Requests in flight for data are already owned by the dispatch
461          * queue or the device driver.  Just restore for normal completion.
462          */
463         list_for_each_entry_safe(rq, n, &q->flush_data_in_flight, flush.list) {
464                 list_del_init(&rq->flush.list);
465                 blk_flush_restore_request(rq);
466         }
467 
468         /*
469          * We need to give away requests on flush queues.  Restore for
470          * normal completion and put them on the dispatch queue.
471          */
472         for (i = 0; i < ARRAY_SIZE(q->flush_queue); i++) {
473                 list_for_each_entry_safe(rq, n, &q->flush_queue[i],
474                                          flush.list) {
475                         list_del_init(&rq->flush.list);
476                         blk_flush_restore_request(rq);
477                         list_add_tail(&rq->queuelist, &q->queue_head);
478                 }
479         }
480 }
481 
482 /**
483  * blkdev_issue_flush - queue a flush
484  * @bdev:       blockdev to issue flush for
485  * @gfp_mask:   memory allocation flags (for bio_alloc)
486  * @error_sector:       error sector
487  *
488  * Description:
489  *    Issue a flush for the block device in question. Caller can supply
490  *    room for storing the error offset in case of a flush error, if they
491  *    wish to. If WAIT flag is not passed then caller may check only what
492  *    request was pushed in some internal queue for later handling.
493  */
494 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
495                 sector_t *error_sector)
496 {
497         struct request_queue *q;
498         struct bio *bio;
499         int ret = 0;
500 
501         if (bdev->bd_disk == NULL)
502                 return -ENXIO;
503 
504         q = bdev_get_queue(bdev);
505         if (!q)
506                 return -ENXIO;
507 
508         /*
509          * some block devices may not have their queue correctly set up here
510          * (e.g. loop device without a backing file) and so issuing a flush
511          * here will panic. Ensure there is a request function before issuing
512          * the flush.
513          */
514         if (!q->make_request_fn)
515                 return -ENXIO;
516 
517         bio = bio_alloc(gfp_mask, 0);
518         bio->bi_bdev = bdev;
519 
520         ret = submit_bio_wait(WRITE_FLUSH, bio);
521 
522         /*
523          * The driver must store the error location in ->bi_sector, if
524          * it supports it. For non-stacked drivers, this should be
525          * copied from blk_rq_pos(rq).
526          */
527         if (error_sector)
528                 *error_sector = bio->bi_iter.bi_sector;
529 
530         bio_put(bio);
531         return ret;
532 }
533 EXPORT_SYMBOL(blkdev_issue_flush);
534 
535 void blk_mq_init_flush(struct request_queue *q)
536 {
537         spin_lock_init(&q->mq_flush_lock);
538 }
539 

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