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_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 }