block/blk-flush.c

   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_PREFLUSH makes sense, which
  14  * indicates a simple flush request.  If there is data, REQ_PREFLUSH 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_PREFLUSH 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_PREFLUSH
  27  * is 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  * REQ_OP_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 long 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 & (1UL << QUEUE_FLAG_WC)) {
 106                 if (rq->cmd_flags & REQ_PREFLUSH)
 107                         policy |= REQ_FSEQ_PREFLUSH;
 108                 if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
 109                     (rq->cmd_flags & REQ_FUA))
 110                         policy |= REQ_FSEQ_POSTFLUSH;
 111         }
 112         return policy;
 113 }
 114
 115 static unsigned int blk_flush_cur_seq(struct request *rq)
 116 {
 117         return 1 << ffz(rq->flush.seq);
 118 }
 119
 120 static void blk_flush_restore_request(struct request *rq)
 121 {
 122         /*
 123          * After flush data completion, @rq->bio is %NULL but we need to
 124          * complete the bio again.  @rq->biotail is guaranteed to equal the
 125          * original @rq->bio.  Restore it.
 126          */
 127         rq->bio = rq->biotail;
 128
 129         /* make @rq a normal request */
 130         rq->cmd_flags &= ~REQ_FLUSH_SEQ;
 131         rq->end_io = rq->flush.saved_end_io;
 132 }
 133
 134 static bool blk_flush_queue_rq(struct request *rq, bool add_front)
 135 {
 136         if (rq->q->mq_ops) {
 137                 struct request_queue *q = rq->q;
 138
 139                 blk_mq_add_to_requeue_list(rq, add_front);
 140                 blk_mq_kick_requeue_list(q);
 141                 return false;
 142         } else {
 143                 if (add_front)
 144                         list_add(&rq->queuelist, &rq->q->queue_head);
 145                 else
 146                         list_add_tail(&rq->queuelist, &rq->q->queue_head);
 147                 return true;
 148         }
 149 }
 150
 151 /**
 152  * blk_flush_complete_seq - complete flush sequence
 153  * @rq: FLUSH/FUA request being sequenced
 154  * @fq: flush queue
 155  * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
 156  * @error: whether an error occurred
 157  *
 158  * @rq just completed @seq part of its flush sequence, record the
 159  * completion and trigger the next step.
 160  *
 161  * CONTEXT:
 162  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
 163  *
 164  * RETURNS:
 165  * %true if requests were added to the dispatch queue, %false otherwise.
 166  */
 167 static bool blk_flush_complete_seq(struct request *rq,
 168                                    struct blk_flush_queue *fq,
 169                                    unsigned int seq, int error)
 170 {
 171         struct request_queue *q = rq->q;
 172         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 173         bool queued = false, kicked;
 174
 175         BUG_ON(rq->flush.seq & seq);
 176         rq->flush.seq |= seq;
 177
 178         if (likely(!error))
 179                 seq = blk_flush_cur_seq(rq);
 180         else
 181                 seq = REQ_FSEQ_DONE;
 182
 183         switch (seq) {
 184         case REQ_FSEQ_PREFLUSH:
 185         case REQ_FSEQ_POSTFLUSH:
 186                 /* queue for flush */
 187                 if (list_empty(pending))
 188                         fq->flush_pending_since = jiffies;
 189                 list_move_tail(&rq->flush.list, pending);
 190                 break;
 191
 192         case REQ_FSEQ_DATA:
 193                 list_move_tail(&rq->flush.list, &fq->flush_data_in_flight);
 194                 queued = blk_flush_queue_rq(rq, true);
 195                 break;
 196
 197         case REQ_FSEQ_DONE:
 198                 /*
 199                  * @rq was previously adjusted by blk_flush_issue() for
 200                  * flush sequencing and may already have gone through the
 201                  * flush data request completion path.  Restore @rq for
 202                  * normal completion and end it.
 203                  */
 204                 BUG_ON(!list_empty(&rq->queuelist));
 205                 list_del_init(&rq->flush.list);
 206                 blk_flush_restore_request(rq);
 207                 if (q->mq_ops)
 208                         blk_mq_end_request(rq, error);
 209                 else
 210                         __blk_end_request_all(rq, error);
 211                 break;
 212
 213         default:
 214                 BUG();
 215         }
 216
 217         kicked = blk_kick_flush(q, fq);
 218         return kicked | queued;
 219 }
 220
 221 static void flush_end_io(struct request *flush_rq, int error)
 222 {
 223         struct request_queue *q = flush_rq->q;
 224         struct list_head *running;
 225         bool queued = false;
 226         struct request *rq, *n;
 227         unsigned long flags = 0;
 228         struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
 229
 230         if (q->mq_ops) {
 231                 struct blk_mq_hw_ctx *hctx;
 232
 233                 /* release the tag's ownership to the req cloned from */
 234                 spin_lock_irqsave(&fq->mq_flush_lock, flags);
 235                 hctx = blk_mq_map_queue(q, flush_rq->mq_ctx->cpu);
 236                 blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
 237                 flush_rq->tag = -1;
 238         }
 239
 240         running = &fq->flush_queue[fq->flush_running_idx];
 241         BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
 242
 243         /* account completion of the flush request */
 244         fq->flush_running_idx ^= 1;
 245
 246         if (!q->mq_ops)
 247                 elv_completed_request(q, flush_rq);
 248
 249         /* and push the waiting requests to the next stage */
 250         list_for_each_entry_safe(rq, n, running, flush.list) {
 251                 unsigned int seq = blk_flush_cur_seq(rq);
 252
 253                 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
 254                 queued |= blk_flush_complete_seq(rq, fq, seq, error);
 255         }
 256
 257         /*
 258          * Kick the queue to avoid stall for two cases:
 259          * 1. Moving a request silently to empty queue_head may stall the
 260          * queue.
 261          * 2. When flush request is running in non-queueable queue, the
 262          * queue is hold. Restart the queue after flush request is finished
 263          * to avoid stall.
 264          * This function is called from request completion path and calling
 265          * directly into request_fn may confuse the driver.  Always use
 266          * kblockd.
 267          */
 268         if (queued || fq->flush_queue_delayed) {
 269                 WARN_ON(q->mq_ops);
 270                 blk_run_queue_async(q);
 271         }
 272         fq->flush_queue_delayed = 0;
 273         if (q->mq_ops)
 274                 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 275 }
 276
 277 /**
 278  * blk_kick_flush - consider issuing flush request
 279  * @q: request_queue being kicked
 280  * @fq: flush queue
 281  *
 282  * Flush related states of @q have changed, consider issuing flush request.
 283  * Please read the comment at the top of this file for more info.
 284  *
 285  * CONTEXT:
 286  * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
 287  *
 288  * RETURNS:
 289  * %true if flush was issued, %false otherwise.
 290  */
 291 static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq)
 292 {
 293         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 294         struct request *first_rq =
 295                 list_first_entry(pending, struct request, flush.list);
 296         struct request *flush_rq = fq->flush_rq;
 297
 298         /* C1 described at the top of this file */
 299         if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
 300                 return false;
 301
 302         /* C2 and C3 */
 303         if (!list_empty(&fq->flush_data_in_flight) &&
 304             time_before(jiffies,
 305                         fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
 306                 return false;
 307
 308         /*
 309          * Issue flush and toggle pending_idx.  This makes pending_idx
 310          * different from running_idx, which means flush is in flight.
 311          */
 312         fq->flush_pending_idx ^= 1;
 313
 314         blk_rq_init(q, flush_rq);
 315
 316         /*
 317          * Borrow tag from the first request since they can't
 318          * be in flight at the same time. And acquire the tag's
 319          * ownership for flush req.
 320          */
 321         if (q->mq_ops) {
 322                 struct blk_mq_hw_ctx *hctx;
 323
 324                 flush_rq->mq_ctx = first_rq->mq_ctx;
 325                 flush_rq->tag = first_rq->tag;
 326                 fq->orig_rq = first_rq;
 327
 328                 hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
 329                 blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
 330         }
 331
 332         flush_rq->cmd_type = REQ_TYPE_FS;
 333         req_set_op_attrs(flush_rq, REQ_OP_FLUSH, WRITE_FLUSH | REQ_FLUSH_SEQ);
 334         flush_rq->rq_disk = first_rq->rq_disk;
 335         flush_rq->end_io = flush_end_io;
 336
 337         return blk_flush_queue_rq(flush_rq, false);
 338 }
 339
 340 static void flush_data_end_io(struct request *rq, int error)
 341 {
 342         struct request_queue *q = rq->q;
 343         struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
 344
 345         /*
 346          * Updating q->in_flight[] here for making this tag usable
 347          * early. Because in blk_queue_start_tag(),
 348          * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
 349          * reserve tags for sync I/O.
 350          *
 351          * More importantly this way can avoid the following I/O
 352          * deadlock:
 353          *
 354          * - suppose there are 40 fua requests comming to flush queue
 355          *   and queue depth is 31
 356          * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
 357          *   tag for async I/O any more
 358          * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
 359          *   and flush_data_end_io() is called
 360          * - the other rqs still can't go ahead if not updating
 361          *   q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
 362          *   are held in flush data queue and make no progress of
 363          *   handling post flush rq
 364          * - only after the post flush rq is handled, all these rqs
 365          *   can be completed
 366          */
 367
 368         elv_completed_request(q, rq);
 369
 370         /* for avoiding double accounting */
 371         rq->cmd_flags &= ~REQ_STARTED;
 372
 373         /*
 374          * After populating an empty queue, kick it to avoid stall.  Read
 375          * the comment in flush_end_io().
 376          */
 377         if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
 378                 blk_run_queue_async(q);
 379 }
 380
 381 static void mq_flush_data_end_io(struct request *rq, int error)
 382 {
 383         struct request_queue *q = rq->q;
 384         struct blk_mq_hw_ctx *hctx;
 385         struct blk_mq_ctx *ctx = rq->mq_ctx;
 386         unsigned long flags;
 387         struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
 388
 389         hctx = blk_mq_map_queue(q, ctx->cpu);
 390
 391         /*
 392          * After populating an empty queue, kick it to avoid stall.  Read
 393          * the comment in flush_end_io().
 394          */
 395         spin_lock_irqsave(&fq->mq_flush_lock, flags);
 396         if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
 397                 blk_mq_run_hw_queue(hctx, true);
 398         spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 399 }
 400
 401 /**
 402  * blk_insert_flush - insert a new FLUSH/FUA request
 403  * @rq: request to insert
 404  *
 405  * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
 406  * or __blk_mq_run_hw_queue() to dispatch request.
 407  * @rq is being submitted.  Analyze what needs to be done and put it on the
 408  * right queue.
 409  *
 410  * CONTEXT:
 411  * spin_lock_irq(q->queue_lock) in !mq case
 412  */
 413 void blk_insert_flush(struct request *rq)
 414 {
 415         struct request_queue *q = rq->q;
 416         unsigned long fflags = q->queue_flags;  /* may change, cache */
 417         unsigned int policy = blk_flush_policy(fflags, rq);
 418         struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
 419
 420         /*
 421          * @policy now records what operations need to be done.  Adjust
 422          * REQ_PREFLUSH and FUA for the driver.
 423          */
 424         rq->cmd_flags &= ~REQ_PREFLUSH;
 425         if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
 426                 rq->cmd_flags &= ~REQ_FUA;
 427
 428         /*
 429          * An empty flush handed down from a stacking driver may
 430          * translate into nothing if the underlying device does not
 431          * advertise a write-back cache.  In this case, simply
 432          * complete the request.
 433          */
 434         if (!policy) {
 435                 if (q->mq_ops)
 436                         blk_mq_end_request(rq, 0);
 437                 else
 438                         __blk_end_bidi_request(rq, 0, 0, 0);
 439                 return;
 440         }
 441
 442         BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
 443
 444         /*
 445          * If there's data but flush is not necessary, the request can be
 446          * processed directly without going through flush machinery.  Queue
 447          * for normal execution.
 448          */
 449         if ((policy & REQ_FSEQ_DATA) &&
 450             !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
 451                 if (q->mq_ops) {
 452                         blk_mq_insert_request(rq, false, false, true);
 453                 } else
 454                         list_add_tail(&rq->queuelist, &q->queue_head);
 455                 return;
 456         }
 457
 458         /*
 459          * @rq should go through flush machinery.  Mark it part of flush
 460          * sequence and submit for further processing.
 461          */
 462         memset(&rq->flush, 0, sizeof(rq->flush));
 463         INIT_LIST_HEAD(&rq->flush.list);
 464         rq->cmd_flags |= REQ_FLUSH_SEQ;
 465         rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
 466         if (q->mq_ops) {
 467                 rq->end_io = mq_flush_data_end_io;
 468
 469                 spin_lock_irq(&fq->mq_flush_lock);
 470                 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
 471                 spin_unlock_irq(&fq->mq_flush_lock);
 472                 return;
 473         }
 474         rq->end_io = flush_data_end_io;
 475
 476         blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
 477 }
 478
 479 /**
 480  * blkdev_issue_flush - queue a flush
 481  * @bdev:       blockdev to issue flush for
 482  * @gfp_mask:   memory allocation flags (for bio_alloc)
 483  * @error_sector:       error sector
 484  *
 485  * Description:
 486  *    Issue a flush for the block device in question. Caller can supply
 487  *    room for storing the error offset in case of a flush error, if they
 488  *    wish to. If WAIT flag is not passed then caller may check only what
 489  *    request was pushed in some internal queue for later handling.
 490  */
 491 int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 492                 sector_t *error_sector)
 493 {
 494         struct request_queue *q;
 495         struct bio *bio;
 496         int ret = 0;
 497
 498         if (bdev->bd_disk == NULL)
 499                 return -ENXIO;
 500
 501         q = bdev_get_queue(bdev);
 502         if (!q)
 503                 return -ENXIO;
 504
 505         /*
 506          * some block devices may not have their queue correctly set up here
 507          * (e.g. loop device without a backing file) and so issuing a flush
 508          * here will panic. Ensure there is a request function before issuing
 509          * the flush.
 510          */
 511         if (!q->make_request_fn)
 512                 return -ENXIO;
 513
 514         bio = bio_alloc(gfp_mask, 0);
 515         bio->bi_bdev = bdev;
 516         bio_set_op_attrs(bio, REQ_OP_WRITE, WRITE_FLUSH);
 517
 518         ret = submit_bio_wait(bio);
 519
 520         /*
 521          * The driver must store the error location in ->bi_sector, if
 522          * it supports it. For non-stacked drivers, this should be
 523          * copied from blk_rq_pos(rq).
 524          */
 525         if (error_sector)
 526                 *error_sector = bio->bi_iter.bi_sector;
 527
 528         bio_put(bio);
 529         return ret;
 530 }
 531 EXPORT_SYMBOL(blkdev_issue_flush);
 532
 533 struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
 534                 int node, int cmd_size)
 535 {
 536         struct blk_flush_queue *fq;
 537         int rq_sz = sizeof(struct request);
 538
 539         fq = kzalloc_node(sizeof(*fq), GFP_KERNEL, node);
 540         if (!fq)
 541                 goto fail;
 542
 543         if (q->mq_ops) {
 544                 spin_lock_init(&fq->mq_flush_lock);
 545                 rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
 546         }
 547
 548         fq->flush_rq = kzalloc_node(rq_sz, GFP_KERNEL, node);
 549         if (!fq->flush_rq)
 550                 goto fail_rq;
 551
 552         INIT_LIST_HEAD(&fq->flush_queue[0]);
 553         INIT_LIST_HEAD(&fq->flush_queue[1]);
 554         INIT_LIST_HEAD(&fq->flush_data_in_flight);
 555
 556         return fq;
 557
 558  fail_rq:
 559         kfree(fq);
 560  fail:
 561         return NULL;
 562 }
 563
 564 void blk_free_flush_queue(struct blk_flush_queue *fq)
 565 {
 566         /* bio based request queue hasn't flush queue */
 567         if (!fq)
 568                 return;
 569
 570         kfree(fq->flush_rq);
 571         kfree(fq);
 572 }