linux/block/blk-flush.c
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   1/*
   2 * Functions to sequence PREFLUSH 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_{PREFLUSH|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, PREFLUSH and FUA don't make any
  20 * difference.  The requests are either completed immediately if there's no data
  21 * 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 PREFLUSH/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 PREFLUSH) 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 PREFLUSH/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 RQF_FLUSH_SEQ in
  60 * req_bio_endio().
  61 *
  62 * The above peculiarity requires that each PREFLUSH/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#include "blk-mq-sched.h"
  78
  79/* PREFLUSH/FUA sequences */
  80enum {
  81        REQ_FSEQ_PREFLUSH       = (1 << 0), /* pre-flushing in progress */
  82        REQ_FSEQ_DATA           = (1 << 1), /* data write in progress */
  83        REQ_FSEQ_POSTFLUSH      = (1 << 2), /* post-flushing in progress */
  84        REQ_FSEQ_DONE           = (1 << 3),
  85
  86        REQ_FSEQ_ACTIONS        = REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |
  87                                  REQ_FSEQ_POSTFLUSH,
  88
  89        /*
  90         * If flush has been pending longer than the following timeout,
  91         * it's issued even if flush_data requests are still in flight.
  92         */
  93        FLUSH_PENDING_TIMEOUT   = 5 * HZ,
  94};
  95
  96static bool blk_kick_flush(struct request_queue *q,
  97                           struct blk_flush_queue *fq, unsigned int flags);
  98
  99static unsigned int blk_flush_policy(unsigned long fflags, struct request *rq)
 100{
 101        unsigned int policy = 0;
 102
 103        if (blk_rq_sectors(rq))
 104                policy |= REQ_FSEQ_DATA;
 105
 106        if (fflags & (1UL << QUEUE_FLAG_WC)) {
 107                if (rq->cmd_flags & REQ_PREFLUSH)
 108                        policy |= REQ_FSEQ_PREFLUSH;
 109                if (!(fflags & (1UL << QUEUE_FLAG_FUA)) &&
 110                    (rq->cmd_flags & REQ_FUA))
 111                        policy |= REQ_FSEQ_POSTFLUSH;
 112        }
 113        return policy;
 114}
 115
 116static unsigned int blk_flush_cur_seq(struct request *rq)
 117{
 118        return 1 << ffz(rq->flush.seq);
 119}
 120
 121static void blk_flush_restore_request(struct request *rq)
 122{
 123        /*
 124         * After flush data completion, @rq->bio is %NULL but we need to
 125         * complete the bio again.  @rq->biotail is guaranteed to equal the
 126         * original @rq->bio.  Restore it.
 127         */
 128        rq->bio = rq->biotail;
 129
 130        /* make @rq a normal request */
 131        rq->rq_flags &= ~RQF_FLUSH_SEQ;
 132        rq->end_io = rq->flush.saved_end_io;
 133}
 134
 135static bool blk_flush_queue_rq(struct request *rq, bool add_front)
 136{
 137        if (rq->q->mq_ops) {
 138                blk_mq_add_to_requeue_list(rq, add_front, true);
 139                return false;
 140        } else {
 141                if (add_front)
 142                        list_add(&rq->queuelist, &rq->q->queue_head);
 143                else
 144                        list_add_tail(&rq->queuelist, &rq->q->queue_head);
 145                return true;
 146        }
 147}
 148
 149/**
 150 * blk_flush_complete_seq - complete flush sequence
 151 * @rq: PREFLUSH/FUA request being sequenced
 152 * @fq: flush queue
 153 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
 154 * @error: whether an error occurred
 155 *
 156 * @rq just completed @seq part of its flush sequence, record the
 157 * completion and trigger the next step.
 158 *
 159 * CONTEXT:
 160 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
 161 *
 162 * RETURNS:
 163 * %true if requests were added to the dispatch queue, %false otherwise.
 164 */
 165static bool blk_flush_complete_seq(struct request *rq,
 166                                   struct blk_flush_queue *fq,
 167                                   unsigned int seq, blk_status_t error)
 168{
 169        struct request_queue *q = rq->q;
 170        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 171        bool queued = false, kicked;
 172        unsigned int cmd_flags;
 173
 174        BUG_ON(rq->flush.seq & seq);
 175        rq->flush.seq |= seq;
 176        cmd_flags = rq->cmd_flags;
 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, cmd_flags);
 218        return kicked | queued;
 219}
 220
 221static void flush_end_io(struct request *flush_rq, blk_status_t 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                if (!q->elevator) {
 237                        blk_mq_tag_set_rq(hctx, flush_rq->tag, fq->orig_rq);
 238                        flush_rq->tag = -1;
 239                } else {
 240                        blk_mq_put_driver_tag_hctx(hctx, flush_rq);
 241                        flush_rq->internal_tag = -1;
 242                }
 243        }
 244
 245        running = &fq->flush_queue[fq->flush_running_idx];
 246        BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
 247
 248        /* account completion of the flush request */
 249        fq->flush_running_idx ^= 1;
 250
 251        if (!q->mq_ops)
 252                elv_completed_request(q, flush_rq);
 253
 254        /* and push the waiting requests to the next stage */
 255        list_for_each_entry_safe(rq, n, running, flush.list) {
 256                unsigned int seq = blk_flush_cur_seq(rq);
 257
 258                BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
 259                queued |= blk_flush_complete_seq(rq, fq, seq, error);
 260        }
 261
 262        /*
 263         * Kick the queue to avoid stall for two cases:
 264         * 1. Moving a request silently to empty queue_head may stall the
 265         * queue.
 266         * 2. When flush request is running in non-queueable queue, the
 267         * queue is hold. Restart the queue after flush request is finished
 268         * to avoid stall.
 269         * This function is called from request completion path and calling
 270         * directly into request_fn may confuse the driver.  Always use
 271         * kblockd.
 272         */
 273        if (queued || fq->flush_queue_delayed) {
 274                WARN_ON(q->mq_ops);
 275                blk_run_queue_async(q);
 276        }
 277        fq->flush_queue_delayed = 0;
 278        if (q->mq_ops)
 279                spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 280}
 281
 282/**
 283 * blk_kick_flush - consider issuing flush request
 284 * @q: request_queue being kicked
 285 * @fq: flush queue
 286 * @flags: cmd_flags of the original request
 287 *
 288 * Flush related states of @q have changed, consider issuing flush request.
 289 * Please read the comment at the top of this file for more info.
 290 *
 291 * CONTEXT:
 292 * spin_lock_irq(q->queue_lock or fq->mq_flush_lock)
 293 *
 294 * RETURNS:
 295 * %true if flush was issued, %false otherwise.
 296 */
 297static bool blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
 298                           unsigned int flags)
 299{
 300        struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 301        struct request *first_rq =
 302                list_first_entry(pending, struct request, flush.list);
 303        struct request *flush_rq = fq->flush_rq;
 304
 305        /* C1 described at the top of this file */
 306        if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
 307                return false;
 308
 309        /* C2 and C3
 310         *
 311         * For blk-mq + scheduling, we can risk having all driver tags
 312         * assigned to empty flushes, and we deadlock if we are expecting
 313         * other requests to make progress. Don't defer for that case.
 314         */
 315        if (!list_empty(&fq->flush_data_in_flight) &&
 316            !(q->mq_ops && q->elevator) &&
 317            time_before(jiffies,
 318                        fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
 319                return false;
 320
 321        /*
 322         * Issue flush and toggle pending_idx.  This makes pending_idx
 323         * different from running_idx, which means flush is in flight.
 324         */
 325        fq->flush_pending_idx ^= 1;
 326
 327        blk_rq_init(q, flush_rq);
 328
 329        /*
 330         * In case of none scheduler, borrow tag from the first request
 331         * since they can't be in flight at the same time. And acquire
 332         * the tag's ownership for flush req.
 333         *
 334         * In case of IO scheduler, flush rq need to borrow scheduler tag
 335         * just for cheating put/get driver tag.
 336         */
 337        if (q->mq_ops) {
 338                struct blk_mq_hw_ctx *hctx;
 339
 340                flush_rq->mq_ctx = first_rq->mq_ctx;
 341
 342                if (!q->elevator) {
 343                        fq->orig_rq = first_rq;
 344                        flush_rq->tag = first_rq->tag;
 345                        hctx = blk_mq_map_queue(q, first_rq->mq_ctx->cpu);
 346                        blk_mq_tag_set_rq(hctx, first_rq->tag, flush_rq);
 347                } else {
 348                        flush_rq->internal_tag = first_rq->internal_tag;
 349                }
 350        }
 351
 352        flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
 353        flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
 354        flush_rq->rq_flags |= RQF_FLUSH_SEQ;
 355        flush_rq->rq_disk = first_rq->rq_disk;
 356        flush_rq->end_io = flush_end_io;
 357
 358        return blk_flush_queue_rq(flush_rq, false);
 359}
 360
 361static void flush_data_end_io(struct request *rq, blk_status_t error)
 362{
 363        struct request_queue *q = rq->q;
 364        struct blk_flush_queue *fq = blk_get_flush_queue(q, NULL);
 365
 366        lockdep_assert_held(q->queue_lock);
 367
 368        /*
 369         * Updating q->in_flight[] here for making this tag usable
 370         * early. Because in blk_queue_start_tag(),
 371         * q->in_flight[BLK_RW_ASYNC] is used to limit async I/O and
 372         * reserve tags for sync I/O.
 373         *
 374         * More importantly this way can avoid the following I/O
 375         * deadlock:
 376         *
 377         * - suppose there are 40 fua requests comming to flush queue
 378         *   and queue depth is 31
 379         * - 30 rqs are scheduled then blk_queue_start_tag() can't alloc
 380         *   tag for async I/O any more
 381         * - all the 30 rqs are completed before FLUSH_PENDING_TIMEOUT
 382         *   and flush_data_end_io() is called
 383         * - the other rqs still can't go ahead if not updating
 384         *   q->in_flight[BLK_RW_ASYNC] here, meantime these rqs
 385         *   are held in flush data queue and make no progress of
 386         *   handling post flush rq
 387         * - only after the post flush rq is handled, all these rqs
 388         *   can be completed
 389         */
 390
 391        elv_completed_request(q, rq);
 392
 393        /* for avoiding double accounting */
 394        rq->rq_flags &= ~RQF_STARTED;
 395
 396        /*
 397         * After populating an empty queue, kick it to avoid stall.  Read
 398         * the comment in flush_end_io().
 399         */
 400        if (blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error))
 401                blk_run_queue_async(q);
 402}
 403
 404static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
 405{
 406        struct request_queue *q = rq->q;
 407        struct blk_mq_hw_ctx *hctx;
 408        struct blk_mq_ctx *ctx = rq->mq_ctx;
 409        unsigned long flags;
 410        struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
 411
 412        hctx = blk_mq_map_queue(q, ctx->cpu);
 413
 414        if (q->elevator) {
 415                WARN_ON(rq->tag < 0);
 416                blk_mq_put_driver_tag_hctx(hctx, rq);
 417        }
 418
 419        /*
 420         * After populating an empty queue, kick it to avoid stall.  Read
 421         * the comment in flush_end_io().
 422         */
 423        spin_lock_irqsave(&fq->mq_flush_lock, flags);
 424        blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
 425        spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 426
 427        blk_mq_run_hw_queue(hctx, true);
 428}
 429
 430/**
 431 * blk_insert_flush - insert a new PREFLUSH/FUA request
 432 * @rq: request to insert
 433 *
 434 * To be called from __elv_add_request() for %ELEVATOR_INSERT_FLUSH insertions.
 435 * or __blk_mq_run_hw_queue() to dispatch request.
 436 * @rq is being submitted.  Analyze what needs to be done and put it on the
 437 * right queue.
 438 */
 439void blk_insert_flush(struct request *rq)
 440{
 441        struct request_queue *q = rq->q;
 442        unsigned long fflags = q->queue_flags;  /* may change, cache */
 443        unsigned int policy = blk_flush_policy(fflags, rq);
 444        struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
 445
 446        if (!q->mq_ops)
 447                lockdep_assert_held(q->queue_lock);
 448
 449        /*
 450         * @policy now records what operations need to be done.  Adjust
 451         * REQ_PREFLUSH and FUA for the driver.
 452         */
 453        rq->cmd_flags &= ~REQ_PREFLUSH;
 454        if (!(fflags & (1UL << QUEUE_FLAG_FUA)))
 455                rq->cmd_flags &= ~REQ_FUA;
 456
 457        /*
 458         * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
 459         * of those flags, we have to set REQ_SYNC to avoid skewing
 460         * the request accounting.
 461         */
 462        rq->cmd_flags |= REQ_SYNC;
 463
 464        /*
 465         * An empty flush handed down from a stacking driver may
 466         * translate into nothing if the underlying device does not
 467         * advertise a write-back cache.  In this case, simply
 468         * complete the request.
 469         */
 470        if (!policy) {
 471                if (q->mq_ops)
 472                        blk_mq_end_request(rq, 0);
 473                else
 474                        __blk_end_request(rq, 0, 0);
 475                return;
 476        }
 477
 478        BUG_ON(rq->bio != rq->biotail); /*assumes zero or single bio rq */
 479
 480        /*
 481         * If there's data but flush is not necessary, the request can be
 482         * processed directly without going through flush machinery.  Queue
 483         * for normal execution.
 484         */
 485        if ((policy & REQ_FSEQ_DATA) &&
 486            !(policy & (REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH))) {
 487                if (q->mq_ops)
 488                        blk_mq_request_bypass_insert(rq, false);
 489                else
 490                        list_add_tail(&rq->queuelist, &q->queue_head);
 491                return;
 492        }
 493
 494        /*
 495         * @rq should go through flush machinery.  Mark it part of flush
 496         * sequence and submit for further processing.
 497         */
 498        memset(&rq->flush, 0, sizeof(rq->flush));
 499        INIT_LIST_HEAD(&rq->flush.list);
 500        rq->rq_flags |= RQF_FLUSH_SEQ;
 501        rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
 502        if (q->mq_ops) {
 503                rq->end_io = mq_flush_data_end_io;
 504
 505                spin_lock_irq(&fq->mq_flush_lock);
 506                blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
 507                spin_unlock_irq(&fq->mq_flush_lock);
 508                return;
 509        }
 510        rq->end_io = flush_data_end_io;
 511
 512        blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
 513}
 514
 515/**
 516 * blkdev_issue_flush - queue a flush
 517 * @bdev:       blockdev to issue flush for
 518 * @gfp_mask:   memory allocation flags (for bio_alloc)
 519 * @error_sector:       error sector
 520 *
 521 * Description:
 522 *    Issue a flush for the block device in question. Caller can supply
 523 *    room for storing the error offset in case of a flush error, if they
 524 *    wish to.
 525 */
 526int blkdev_issue_flush(struct block_device *bdev, gfp_t gfp_mask,
 527                sector_t *error_sector)
 528{
 529        struct request_queue *q;
 530        struct bio *bio;
 531        int ret = 0;
 532
 533        if (bdev->bd_disk == NULL)
 534                return -ENXIO;
 535
 536        q = bdev_get_queue(bdev);
 537        if (!q)
 538                return -ENXIO;
 539
 540        /*
 541         * some block devices may not have their queue correctly set up here
 542         * (e.g. loop device without a backing file) and so issuing a flush
 543         * here will panic. Ensure there is a request function before issuing
 544         * the flush.
 545         */
 546        if (!q->make_request_fn)
 547                return -ENXIO;
 548
 549        bio = bio_alloc(gfp_mask, 0);
 550        bio_set_dev(bio, bdev);
 551        bio->bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
 552
 553        ret = submit_bio_wait(bio);
 554
 555        /*
 556         * The driver must store the error location in ->bi_sector, if
 557         * it supports it. For non-stacked drivers, this should be
 558         * copied from blk_rq_pos(rq).
 559         */
 560        if (error_sector)
 561                *error_sector = bio->bi_iter.bi_sector;
 562
 563        bio_put(bio);
 564        return ret;
 565}
 566EXPORT_SYMBOL(blkdev_issue_flush);
 567
 568struct blk_flush_queue *blk_alloc_flush_queue(struct request_queue *q,
 569                int node, int cmd_size, gfp_t flags)
 570{
 571        struct blk_flush_queue *fq;
 572        int rq_sz = sizeof(struct request);
 573
 574        fq = kzalloc_node(sizeof(*fq), flags, node);
 575        if (!fq)
 576                goto fail;
 577
 578        if (q->mq_ops)
 579                spin_lock_init(&fq->mq_flush_lock);
 580
 581        rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
 582        fq->flush_rq = kzalloc_node(rq_sz, flags, node);
 583        if (!fq->flush_rq)
 584                goto fail_rq;
 585
 586        INIT_LIST_HEAD(&fq->flush_queue[0]);
 587        INIT_LIST_HEAD(&fq->flush_queue[1]);
 588        INIT_LIST_HEAD(&fq->flush_data_in_flight);
 589
 590        return fq;
 591
 592 fail_rq:
 593        kfree(fq);
 594 fail:
 595        return NULL;
 596}
 597
 598void blk_free_flush_queue(struct blk_flush_queue *fq)
 599{
 600        /* bio based request queue hasn't flush queue */
 601        if (!fq)
 602                return;
 603
 604        kfree(fq->flush_rq);
 605        kfree(fq);
 606}
 607