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TOMOYO Linux Cross Reference
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  * fq->flush_queue[fq->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 #include "blk-mq-tag.h"
 77 
 78 /* FLUSH/FUA sequences */
 79 enum {
 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),
 84 
 85         REQ_FSEQ_ACTIONS        = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
 86                                   REQ_FSEQ_POSTFLUSH,
 87 
 88         /*
 89          * If flush has been pending longer than the following timeout,
 90          * it's issued even if flush_data requests are still in flight.
 91          */
 92         FLUSH_PENDING_TIMEOUT   = 5 * HZ,
 93 };
 94 
 95 static bool blk_kick_flush(struct request_queue *q,
 96                            struct blk_flush_queue *fq);
 97 
 98 static unsigned int blk_flush_policy(unsigned int fflags, struct request *rq)
 99 {
100         unsigned int policy = 0;
101 
102         if (blk_rq_sectors(rq))
103                 policy |= REQ_FSEQ_DATA;
104 
105         if (fflags & REQ_FLUSH) {
106                 if (rq->cmd_flags & REQ_FLUSH)
107                         policy |= REQ_FSEQ_PREFLUSH;
108                 if (!(fflags & REQ_FUA) && (rq->cmd_flags & REQ_FUA))
109                         policy |= REQ_FSEQ_POSTFLUSH;
110         }
111         return policy;
112 }
113 
114 static unsigned int blk_flush_cur_seq(struct request *rq)
115 {
116         return 1 << ffz(rq->flush.seq);
117 }
118 
119 static void blk_flush_restore_request(struct request *rq)
120 {
121         /*
122          * After flush data completion, @rq->bio is %NULL but we need to
123          * complete the bio again.  @rq->biotail is guaranteed to equal the
124          * original @rq->bio.  Restore it.
125          */
126         rq->bio = rq->biotail;
127 
128         /* make @rq a normal request */
129         rq->cmd_flags &= ~REQ_FLUSH_SEQ;
130         rq->end_io = rq->flush.saved_end_io;
131 }
132 
133 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
134 {
135         if (rq->q->mq_ops) {
136                 struct request_queue *q = rq->q;
137 
138                 blk_mq_add_to_requeue_list(rq, add_front);
139                 blk_mq_kick_requeue_list(q);
140                 return false;
141         } else {
142                 if (add_front)
143                         list_add(&rq->queuelist, &rq->q->queue_head);
144                 else
145                         list_add_tail(&rq->queuelist, &rq->q->queue_head);
146                 return true;
147         }
148 }
149 
150 /**
151  * blk_flush_complete_seq - complete flush sequence
152  * @rq: FLUSH/FUA request being sequenced
153  * @fq: flush queue
154  * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
155  * @error: whether an error occurred
156  *
157  * @rq just completed @seq part of its flush sequence, record the
158  * completion and trigger the next step.
159  *
160  * CONTEXT:
161  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
162  *
163  * RETURNS:
164  * %true if requests were added to the dispatch queue, %false otherwise.
165  */
166 static bool blk_flush_complete_seq(struct request *rq,
167                                    struct blk_flush_queue *fq,
168                                    unsigned int seq, int error)
169 {
170         struct request_queue *q = rq->q;
171         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
172         bool queued = false, kicked;
173 
174         BUG_ON(rq->flush.seq & seq);
175         rq->flush.seq |= seq;
176 
177         if (likely(!error))
178                 seq = blk_flush_cur_seq(rq);
179         else
180                 seq = REQ_FSEQ_DONE;
181 
182         switch (seq) {
183         case REQ_FSEQ_PREFLUSH:
184         case REQ_FSEQ_POSTFLUSH:
185                 /* queue for flush */
186                 if (list_empty(pending))
187                         fq->flush_pending_since = jiffies;
188                 list_move_tail(&rq->flush.list, pending);
189                 break;
190 
191         case REQ_FSEQ_DATA:
192                 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
193                 queued = blk_flush_queue_rq(rq, true);
194                 break;
195 
196         case REQ_FSEQ_DONE:
197                 /*
198                  * @rq was previously adjusted by blk_flush_issue() for
199                  * flush sequencing and may already have gone through the
200                  * flush data request completion path.  Restore @rq for
201                  * normal completion and end it.
202                  */
203                 BUG_ON(!list_empty(&rq->queuelist));
204                 list_del_init(&rq->flush.list);
205                 blk_flush_restore_request(rq);
206                 if (q->mq_ops)
207                         blk_mq_end_request(rq, error);
208                 else
209                         __blk_end_request_all(rq, error);
210                 break;
211 
212         default:
213                 BUG();
214         }
215 
216         kicked = blk_kick_flush(q, fq);
217         return kicked | queued;
218 }
219 
220 static void flush_end_io(struct request *flush_rq, int error)
221 {
222         struct request_queue *q = flush_rq->q;
223         struct list_head *running;
224         bool queued = false;
225         struct request *rq, *n;
226         unsigned long flags = 0;
227         struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
228 
229         if (q->mq_ops) {
230                 struct blk_mq_hw_ctx *hctx;
231 
232                 /* release the tag's ownership to the req cloned from */
233                 spin_lock_irqsave(&fq->mq_flush_lock, flags);
234                 hctx = q->mq_ops->map_queue(q, flush_rq->mq_ctx->cpu);
235                 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
236                 flush_rq->tag = -1;
237         }
238 
239         running = &fq->flush_queue[fq->flush_running_idx];
240         BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
241 
242         /* account completion of the flush request */
243         fq->flush_running_idx ^= 1;
244 
245         if (!q->mq_ops)
246                 elv_completed_request(q, flush_rq);
247 
248         /* and push the waiting requests to the next stage */
249         list_for_each_entry_safe(rq, n, running, flush.list) {
250                 unsigned int seq = blk_flush_cur_seq(rq);
251 
252                 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
253                 queued |= blk_flush_complete_seq(rq, fq, seq, error);
254         }
255 
256         /*
257          * Kick the queue to avoid stall for two cases:
258          * 1. Moving a request silently to empty queue_head may stall the
259          * queue.
260          * 2. When flush request is running in non-queueable queue, the
261          * queue is hold. Restart the queue after flush request is finished
262          * to avoid stall.
263          * This function is called from request completion path and calling
264          * directly into request_fn may confuse the driver.  Always use
265          * kblockd.
266          */
267         if (queued || fq->flush_queue_delayed) {
268                 WARN_ON(q->mq_ops);
269                 blk_run_queue_async(q);
270         }
271         fq->flush_queue_delayed = 0;
272         if (q->mq_ops)
273                 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
274 }
275 
276 /**
277  * blk_kick_flush - consider issuing flush request
278  * @q: request_queue being kicked
279  * @fq: flush queue
280  *
281  * Flush related states of @q have changed, consider issuing flush request.
282  * Please read the comment at the top of this file for more info.
283  *
284  * CONTEXT:
285  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
286  *
287  * RETURNS:
288  * %true if flush was issued, %false otherwise.
289  */
290 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
291 {
292         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
293         struct request *first_rq =
294                 list_first_entry(pending, struct request, flush.list);
295         struct request *flush_rq = fq->flush_rq;
296 
297         /* C1 described at the top of this file */
298         if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
299                 return false;
300 
301         /* C2 and C3 */
302         if (!list_empty(&fq->flush_data_in_flight) &&
303             time_before(jiffies,
304                         fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
305                 return false;
306 
307         /*
308          * Issue flush and toggle pending_idx.  This makes pending_idx
309          * different from running_idx, which means flush is in flight.
310          */
311         fq->flush_pending_idx ^= 1;
312 
313         blk_rq_init(q, flush_rq);
314 
315         /*
316          * Borrow tag from the first request since they can't
317          * be in flight at the same time. And acquire the tag's
318          * ownership for flush req.
319          */
320         if (q->mq_ops) {
321                 struct blk_mq_hw_ctx *hctx;
322 
323                 flush_rq->mq_ctx = first_rq->mq_ctx;
324                 flush_rq->tag = first_rq->tag;
325                 fq->orig_rq = first_rq;
326 
327                 hctx = q->mq_ops->map_queue(q, first_rq->mq_ctx->cpu);
328                 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
329         }
330 
331         flush_rq->cmd_type = REQ_TYPE_FS;
332         flush_rq->cmd_flags = WRITE_FLUSH | REQ_FLUSH_SEQ;
333         flush_rq->rq_disk = first_rq->rq_disk;
334         flush_rq->end_io = flush_end_io;
335 
336         return blk_flush_queue_rq(flush_rq, false);
337 }
338 
339 static void flush_data_end_io(struct request *rq, int error)
340 {
341         struct request_queue *q = rq->q;
342         struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
343 
344         /*
345          * After populating an empty queue, kick it to avoid stall.  Read
346          * the comment in flush_end_io().
347          */
348         if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
349                 blk_run_queue_async(q);
350 }
351 
352 static void mq_flush_data_end_io(struct request *rq, int error)
353 {
354         struct request_queue *q = rq->q;
355         struct blk_mq_hw_ctx *hctx;
356         struct blk_mq_ctx *ctx = rq->mq_ctx;
357         unsigned long flags;
358         struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
359 
360         hctx = q->mq_ops->map_queue(q, ctx->cpu);
361 
362         /*
363          * After populating an empty queue, kick it to avoid stall.  Read
364          * the comment in flush_end_io().
365          */
366         spin_lock_irqsave(&fq->mq_flush_lock, flags);
367         if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
368                 blk_mq_run_hw_queue(hctx, true);
369         spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
370 }
371 
372 /**
373  * blk_insert_flush - insert a new FLUSH/FUA request
374  * @rq: request to insert
375  *
376  * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
377  * or __blk_mq_run_hw_queue() to dispatch request.
378  * @rq is being submitted.  Analyze what needs to be done and put it on the
379  * right queue.
380  *
381  * CONTEXT:
382  * spin_lock_irq(q->queue_lock) in !mq case
383  */
384 void blk_insert_flush(struct request *rq)
385 {
386         struct request_queue *q = rq->q;
387         unsigned int fflags = q->flush_flags;   /* may change, cache */
388         unsigned int policy = blk_flush_policy(fflags, rq);
389         struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
390 
391         /*
392          * @policy now records what operations need to be done.  Adjust
393          * REQ_FLUSH and FUA for the driver.
394          */
395         rq->cmd_flags &= ~REQ_FLUSH;
396         if (!(fflags & REQ_FUA))
397                 rq->cmd_flags &= ~REQ_FUA;
398 
399         /*
400          * An empty flush handed down from a stacking driver may
401          * translate into nothing if the underlying device does not
402          * advertise a write-back cache.  In this case, simply
403          * complete the request.
404          */
405         if (!policy) {
406                 if (q->mq_ops)
407                         blk_mq_end_request(rq, 0);
408                 else
409                         __blk_end_bidi_request(rq, 0, 0, 0);
410                 return;
411         }
412 
413         BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
414 
415         /*
416          * If there's data but flush is not necessary, the request can be
417          * processed directly without going through flush machinery.  Queue
418          * for normal execution.
419          */
420         if ((policy & REQ_FSEQ_DATA) &&
421             !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
422                 if (q->mq_ops) {
423                         blk_mq_insert_request(rq, false, false, true);
424                 } else
425                         list_add_tail(&rq->queuelist, &q->queue_head);
426                 return;
427         }
428 
429         /*
430          * @rq should go through flush machinery.  Mark it part of flush
431          * sequence and submit for further processing.
432          */
433         memset(&rq->flush, 0, sizeof(rq->flush));
434         INIT_LIST_HEAD(&rq->flush.list);
435         rq->cmd_flags |= REQ_FLUSH_SEQ;
436         rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
437         if (q->mq_ops) {
438                 rq->end_io = mq_flush_data_end_io;
439 
440                 spin_lock_irq(&fq->mq_flush_lock);
441                 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
442                 spin_unlock_irq(&fq->mq_flush_lock);
443                 return;
444         }
445         rq->end_io = flush_data_end_io;
446 
447         blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
448 }
449 
450 /**
451  * blkdev_issue_flush - queue a flush
452  * @bdev:       blockdev to issue flush for
453  * @gfp_mask:   memory allocation flags (for bio_alloc)
454  * @error_sector:       error sector
455  *
456  * Description:
457  *    Issue a flush for the block device in question. Caller can supply
458  *    room for storing the error offset in case of a flush error, if they
459  *    wish to. If WAIT flag is not passed then caller may check only what
460  *    request was pushed in some internal queue for later handling.
461  */
462 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
463                 sector_t *error_sector)
464 {
465         struct request_queue *q;
466         struct bio *bio;
467         int ret = 0;
468 
469         if (bdev->bd_disk == NULL)
470                 return -ENXIO;
471 
472         q = bdev_get_queue(bdev);
473         if (!q)
474                 return -ENXIO;
475 
476         /*
477          * some block devices may not have their queue correctly set up here
478          * (e.g. loop device without a backing file) and so issuing a flush
479          * here will panic. Ensure there is a request function before issuing
480          * the flush.
481          */
482         if (!q->make_request_fn)
483                 return -ENXIO;
484 
485         bio = bio_alloc(gfp_mask, 0);
486         bio->bi_bdev = bdev;
487 
488         ret = submit_bio_wait(WRITE_FLUSH, bio);
489 
490         /*
491          * The driver must store the error location in ->bi_sector, if
492          * it supports it. For non-stacked drivers, this should be
493          * copied from blk_rq_pos(rq).
494          */
495         if (error_sector)
496                 *error_sector = bio->bi_iter.bi_sector;
497 
498         bio_put(bio);
499         return ret;
500 }
501 EXPORT_SYMBOL(blkdev_issue_flush);
502 
503 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
504                 int node, int cmd_size)
505 {
506         struct blk_flush_queue *fq;
507         int rq_sz = sizeof(struct request);
508 
509         fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
510         if (!fq)
511                 goto fail;
512 
513         if (q->mq_ops) {
514                 spin_lock_init(&fq->mq_flush_lock);
515                 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
516         }
517 
518         fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
519         if (!fq->flush_rq)
520                 goto fail_rq;
521 
522         INIT_LIST_HEAD(&fq->flush_queue[0]);
523         INIT_LIST_HEAD(&fq->flush_queue[1]);
524         INIT_LIST_HEAD(&fq->flush_data_in_flight);
525 
526         return fq;
527 
528  fail_rq:
529         kfree(fq);
530  fail:
531         return NULL;
532 }
533 
534 void blk_free_flush_queue(struct blk_flush_queue *fq)
535 {
536         /* bio based request queue hasn't flush queue */
537         if (!fq)
538                 return;
539 
540         kfree(fq->flush_rq);
541         kfree(fq);
542 }
543 

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