block/blk-flush.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * Functions to sequence PREFLUSH and FUA writes.
   4  *
   5  * Copyright (C) 2011           Max Planck Institute for Gravitational Physics
   6  * Copyright (C) 2011           Tejun Heo <tj@kernel.org>
   7  *
   8  * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three
   9  * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request
  10  * properties and hardware capability.
  11  *
  12  * If a request doesn't have data, only REQ_PREFLUSH makes sense, which
  13  * indicates a simple flush request.  If there is data, REQ_PREFLUSH indicates
  14  * that the device cache should be flushed before the data is executed, and
  15  * REQ_FUA means that the data must be on non-volatile media on request
  16  * completion.
  17  *
  18  * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any
  19  * difference.  The requests are either completed immediately if there's no data
  20  * or executed as normal requests otherwise.
  21  *
  22  * If the device has writeback cache and supports FUA, REQ_PREFLUSH is
  23  * translated to PREFLUSH but REQ_FUA is passed down directly with DATA.
  24  *
  25  * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH
  26  * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.
  27  *
  28  * The actual execution of flush is double buffered.  Whenever a request
  29  * needs to execute PRE or POSTFLUSH, it queues at
  30  * fq->flush_queue[fq->flush_pending_idx].  Once certain criteria are met, a
  31  * REQ_OP_FLUSH is issued and the pending_idx is toggled.  When the flush
  32  * completes, all the requests which were pending are proceeded to the next
  33  * step.  This allows arbitrary merging of different types of PREFLUSH/FUA
  34  * requests.
  35  *
  36  * Currently, the following conditions are used to determine when to issue
  37  * flush.
  38  *
  39  * C1. At any given time, only one flush shall be in progress.  This makes
  40  *     double buffering sufficient.
  41  *
  42  * C2. Flush is deferred if any request is executing DATA of its sequence.
  43  *     This avoids issuing separate POSTFLUSHes for requests which shared
  44  *     PREFLUSH.
  45  *
  46  * C3. The second condition is ignored if there is a request which has
  47  *     waited longer than FLUSH_PENDING_TIMEOUT.  This is to avoid
  48  *     starvation in the unlikely case where there are continuous stream of
  49  *     FUA (without PREFLUSH) requests.
  50  *
  51  * For devices which support FUA, it isn't clear whether C2 (and thus C3)
  52  * is beneficial.
  53  *
  54  * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice.
  55  * Once while executing DATA and again after the whole sequence is
  56  * complete.  The first completion updates the contained bio but doesn't
  57  * finish it so that the bio submitter is notified only after the whole
  58  * sequence is complete.  This is implemented by testing RQF_FLUSH_SEQ in
  59  * req_bio_endio().
  60  *
  61  * The above peculiarity requires that each PREFLUSH/FUA request has only one
  62  * bio attached to it, which is guaranteed as they aren't allowed to be
  63  * merged in the usual way.
  64  */
  65
  66 #include <linux/kernel.h>
  67 #include <linux/module.h>
  68 #include <linux/bio.h>
  69 #include <linux/blkdev.h>
  70 #include <linux/gfp.h>
  71 #include <linux/part_stat.h>
  72
  73 #include "blk.h"
  74 #include "blk-mq.h"
  75 #include "blk-mq-sched.h"
  76
  77 /* PREFLUSH/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 void blk_kick_flush(struct request_queue *q,
  95                            struct blk_flush_queue *fq, blk_opf_t flags);
  96
  97 static inline struct blk_flush_queue *
  98 blk_get_flush_queue(struct request_queue *q, struct blk_mq_ctx *ctx)
  99 {
 100         return blk_mq_map_queue(q, REQ_OP_FLUSH, ctx)->fq;
 101 }
 102
 103 static unsigned int blk_flush_cur_seq(struct request *rq)
 104 {
 105         return 1 << ffz(rq->flush.seq);
 106 }
 107
 108 static void blk_flush_restore_request(struct request *rq)
 109 {
 110         /*
 111          * After flush data completion, @rq->bio is %NULL but we need to
 112          * complete the bio again.  @rq->biotail is guaranteed to equal the
 113          * original @rq->bio.  Restore it.
 114          */
 115         rq->bio = rq->biotail;
 116         if (rq->bio)
 117                 rq->__sector = rq->bio->bi_iter.bi_sector;
 118
 119         /* make @rq a normal request */
 120         rq->rq_flags &= ~RQF_FLUSH_SEQ;
 121         rq->end_io = rq->flush.saved_end_io;
 122 }
 123
 124 static void blk_account_io_flush(struct request *rq)
 125 {
 126         struct block_device *part = rq->q->disk->part0;
 127
 128         part_stat_lock();
 129         part_stat_inc(part, ios[STAT_FLUSH]);
 130         part_stat_add(part, nsecs[STAT_FLUSH],
 131                       blk_time_get_ns() - rq->start_time_ns);
 132         part_stat_unlock();
 133 }
 134
 135 /**
 136  * blk_flush_complete_seq - complete flush sequence
 137  * @rq: PREFLUSH/FUA request being sequenced
 138  * @fq: flush queue
 139  * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)
 140  * @error: whether an error occurred
 141  *
 142  * @rq just completed @seq part of its flush sequence, record the
 143  * completion and trigger the next step.
 144  *
 145  * CONTEXT:
 146  * spin_lock_irq(fq->mq_flush_lock)
 147  */
 148 static void blk_flush_complete_seq(struct request *rq,
 149                                    struct blk_flush_queue *fq,
 150                                    unsigned int seq, blk_status_t error)
 151 {
 152         struct request_queue *q = rq->q;
 153         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 154         blk_opf_t cmd_flags;
 155
 156         BUG_ON(rq->flush.seq & seq);
 157         rq->flush.seq |= seq;
 158         cmd_flags = rq->cmd_flags;
 159
 160         if (likely(!error))
 161                 seq = blk_flush_cur_seq(rq);
 162         else
 163                 seq = REQ_FSEQ_DONE;
 164
 165         switch (seq) {
 166         case REQ_FSEQ_PREFLUSH:
 167         case REQ_FSEQ_POSTFLUSH:
 168                 /* queue for flush */
 169                 if (list_empty(pending))
 170                         fq->flush_pending_since = jiffies;
 171                 list_add_tail(&rq->queuelist, pending);
 172                 break;
 173
 174         case REQ_FSEQ_DATA:
 175                 fq->flush_data_in_flight++;
 176                 spin_lock(&q->requeue_lock);
 177                 list_move(&rq->queuelist, &q->requeue_list);
 178                 spin_unlock(&q->requeue_lock);
 179                 blk_mq_kick_requeue_list(q);
 180                 break;
 181
 182         case REQ_FSEQ_DONE:
 183                 /*
 184                  * @rq was previously adjusted by blk_insert_flush() for
 185                  * flush sequencing and may already have gone through the
 186                  * flush data request completion path.  Restore @rq for
 187                  * normal completion and end it.
 188                  */
 189                 list_del_init(&rq->queuelist);
 190                 blk_flush_restore_request(rq);
 191                 blk_mq_end_request(rq, error);
 192                 break;
 193
 194         default:
 195                 BUG();
 196         }
 197
 198         blk_kick_flush(q, fq, cmd_flags);
 199 }
 200
 201 static enum rq_end_io_ret flush_end_io(struct request *flush_rq,
 202                                        blk_status_t error)
 203 {
 204         struct request_queue *q = flush_rq->q;
 205         struct list_head *running;
 206         struct request *rq, *n;
 207         unsigned long flags = 0;
 208         struct blk_flush_queue *fq = blk_get_flush_queue(q, flush_rq->mq_ctx);
 209
 210         /* release the tag's ownership to the req cloned from */
 211         spin_lock_irqsave(&fq->mq_flush_lock, flags);
 212
 213         if (!req_ref_put_and_test(flush_rq)) {
 214                 fq->rq_status = error;
 215                 spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 216                 return RQ_END_IO_NONE;
 217         }
 218
 219         blk_account_io_flush(flush_rq);
 220         /*
 221          * Flush request has to be marked as IDLE when it is really ended
 222          * because its .end_io() is called from timeout code path too for
 223          * avoiding use-after-free.
 224          */
 225         WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);
 226         if (fq->rq_status != BLK_STS_OK) {
 227                 error = fq->rq_status;
 228                 fq->rq_status = BLK_STS_OK;
 229         }
 230
 231         if (!q->elevator) {
 232                 flush_rq->tag = BLK_MQ_NO_TAG;
 233         } else {
 234                 blk_mq_put_driver_tag(flush_rq);
 235                 flush_rq->internal_tag = BLK_MQ_NO_TAG;
 236         }
 237
 238         running = &fq->flush_queue[fq->flush_running_idx];
 239         BUG_ON(fq->flush_pending_idx == fq->flush_running_idx);
 240
 241         /* account completion of the flush request */
 242         fq->flush_running_idx ^= 1;
 243
 244         /* and push the waiting requests to the next stage */
 245         list_for_each_entry_safe(rq, n, running, queuelist) {
 246                 unsigned int seq = blk_flush_cur_seq(rq);
 247
 248                 BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);
 249                 list_del_init(&rq->queuelist);
 250                 blk_flush_complete_seq(rq, fq, seq, error);
 251         }
 252
 253         spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 254         return RQ_END_IO_NONE;
 255 }
 256
 257 bool is_flush_rq(struct request *rq)
 258 {
 259         return rq->end_io == flush_end_io;
 260 }
 261
 262 /**
 263  * blk_kick_flush - consider issuing flush request
 264  * @q: request_queue being kicked
 265  * @fq: flush queue
 266  * @flags: cmd_flags of the original request
 267  *
 268  * Flush related states of @q have changed, consider issuing flush request.
 269  * Please read the comment at the top of this file for more info.
 270  *
 271  * CONTEXT:
 272  * spin_lock_irq(fq->mq_flush_lock)
 273  *
 274  */
 275 static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
 276                            blk_opf_t flags)
 277 {
 278         struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];
 279         struct request *first_rq =
 280                 list_first_entry(pending, struct request, queuelist);
 281         struct request *flush_rq = fq->flush_rq;
 282
 283         /* C1 described at the top of this file */
 284         if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
 285                 return;
 286
 287         /* C2 and C3 */
 288         if (fq->flush_data_in_flight &&
 289             time_before(jiffies,
 290                         fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
 291                 return;
 292
 293         /*
 294          * Issue flush and toggle pending_idx.  This makes pending_idx
 295          * different from running_idx, which means flush is in flight.
 296          */
 297         fq->flush_pending_idx ^= 1;
 298
 299         blk_rq_init(q, flush_rq);
 300
 301         /*
 302          * In case of none scheduler, borrow tag from the first request
 303          * since they can't be in flight at the same time. And acquire
 304          * the tag's ownership for flush req.
 305          *
 306          * In case of IO scheduler, flush rq need to borrow scheduler tag
 307          * just for cheating put/get driver tag.
 308          */
 309         flush_rq->mq_ctx = first_rq->mq_ctx;
 310         flush_rq->mq_hctx = first_rq->mq_hctx;
 311
 312         if (!q->elevator)
 313                 flush_rq->tag = first_rq->tag;
 314         else
 315                 flush_rq->internal_tag = first_rq->internal_tag;
 316
 317         flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;
 318         flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);
 319         flush_rq->rq_flags |= RQF_FLUSH_SEQ;
 320         flush_rq->end_io = flush_end_io;
 321         /*
 322          * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one
 323          * implied in refcount_inc_not_zero() called from
 324          * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref
 325          * and READ flush_rq->end_io
 326          */
 327         smp_wmb();
 328         req_ref_set(flush_rq, 1);
 329
 330         spin_lock(&q->requeue_lock);
 331         list_add_tail(&flush_rq->queuelist, &q->flush_list);
 332         spin_unlock(&q->requeue_lock);
 333
 334         blk_mq_kick_requeue_list(q);
 335 }
 336
 337 static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,
 338                                                blk_status_t error)
 339 {
 340         struct request_queue *q = rq->q;
 341         struct blk_mq_hw_ctx *hctx = rq->mq_hctx;
 342         struct blk_mq_ctx *ctx = rq->mq_ctx;
 343         unsigned long flags;
 344         struct blk_flush_queue *fq = blk_get_flush_queue(q, ctx);
 345
 346         if (q->elevator) {
 347                 WARN_ON(rq->tag < 0);
 348                 blk_mq_put_driver_tag(rq);
 349         }
 350
 351         /*
 352          * After populating an empty queue, kick it to avoid stall.  Read
 353          * the comment in flush_end_io().
 354          */
 355         spin_lock_irqsave(&fq->mq_flush_lock, flags);
 356         fq->flush_data_in_flight--;
 357         /*
 358          * May have been corrupted by rq->rq_next reuse, we need to
 359          * re-initialize rq->queuelist before reusing it here.
 360          */
 361         INIT_LIST_HEAD(&rq->queuelist);
 362         blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
 363         spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 364
 365         blk_mq_sched_restart(hctx);
 366         return RQ_END_IO_NONE;
 367 }
 368
 369 static void blk_rq_init_flush(struct request *rq)
 370 {
 371         rq->flush.seq = 0;
 372         rq->rq_flags |= RQF_FLUSH_SEQ;
 373         rq->flush.saved_end_io = rq->end_io; /* Usually NULL */
 374         rq->end_io = mq_flush_data_end_io;
 375 }
 376
 377 /*
 378  * Insert a PREFLUSH/FUA request into the flush state machine.
 379  * Returns true if the request has been consumed by the flush state machine,
 380  * or false if the caller should continue to process it.
 381  */
 382 bool blk_insert_flush(struct request *rq)
 383 {
 384         struct request_queue *q = rq->q;
 385         struct blk_flush_queue *fq = blk_get_flush_queue(q, rq->mq_ctx);
 386         bool supports_fua = q->limits.features & BLK_FEAT_FUA;
 387         unsigned int policy = 0;
 388
 389         /* FLUSH/FUA request must never be merged */
 390         WARN_ON_ONCE(rq->bio != rq->biotail);
 391
 392         if (blk_rq_sectors(rq))
 393                 policy |= REQ_FSEQ_DATA;
 394
 395         /*
 396          * Check which flushes we need to sequence for this operation.
 397          */
 398         if (blk_queue_write_cache(q)) {
 399                 if (rq->cmd_flags & REQ_PREFLUSH)
 400                         policy |= REQ_FSEQ_PREFLUSH;
 401                 if ((rq->cmd_flags & REQ_FUA) && !supports_fua)
 402                         policy |= REQ_FSEQ_POSTFLUSH;
 403         }
 404
 405         /*
 406          * @policy now records what operations need to be done.  Adjust
 407          * REQ_PREFLUSH and FUA for the driver.
 408          */
 409         rq->cmd_flags &= ~REQ_PREFLUSH;
 410         if (!supports_fua)
 411                 rq->cmd_flags &= ~REQ_FUA;
 412
 413         /*
 414          * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any
 415          * of those flags, we have to set REQ_SYNC to avoid skewing
 416          * the request accounting.
 417          */
 418         rq->cmd_flags |= REQ_SYNC;
 419
 420         switch (policy) {
 421         case 0:
 422                 /*
 423                  * An empty flush handed down from a stacking driver may
 424                  * translate into nothing if the underlying device does not
 425                  * advertise a write-back cache.  In this case, simply
 426                  * complete the request.
 427                  */
 428                 blk_mq_end_request(rq, 0);
 429                 return true;
 430         case REQ_FSEQ_DATA:
 431                 /*
 432                  * If there's data, but no flush is necessary, the request can
 433                  * be processed directly without going through flush machinery.
 434                  * Queue for normal execution.
 435                  */
 436                 return false;
 437         case REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH:
 438                 /*
 439                  * Initialize the flush fields and completion handler to trigger
 440                  * the post flush, and then just pass the command on.
 441                  */
 442                 blk_rq_init_flush(rq);
 443                 rq->flush.seq |= REQ_FSEQ_PREFLUSH;
 444                 spin_lock_irq(&fq->mq_flush_lock);
 445                 fq->flush_data_in_flight++;
 446                 spin_unlock_irq(&fq->mq_flush_lock);
 447                 return false;
 448         default:
 449                 /*
 450                  * Mark the request as part of a flush sequence and submit it
 451                  * for further processing to the flush state machine.
 452                  */
 453                 blk_rq_init_flush(rq);
 454                 spin_lock_irq(&fq->mq_flush_lock);
 455                 blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);
 456                 spin_unlock_irq(&fq->mq_flush_lock);
 457                 return true;
 458         }
 459 }
 460
 461 /**
 462  * blkdev_issue_flush - queue a flush
 463  * @bdev:       blockdev to issue flush for
 464  *
 465  * Description:
 466  *    Issue a flush for the block device in question.
 467  */
 468 int blkdev_issue_flush(struct block_device *bdev)
 469 {
 470         struct bio bio;
 471
 472         bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);
 473         return submit_bio_wait(&bio);
 474 }
 475 EXPORT_SYMBOL(blkdev_issue_flush);
 476
 477 struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,
 478                                               gfp_t flags)
 479 {
 480         struct blk_flush_queue *fq;
 481         int rq_sz = sizeof(struct request);
 482
 483         fq = kzalloc_node(sizeof(*fq), flags, node);
 484         if (!fq)
 485                 goto fail;
 486
 487         spin_lock_init(&fq->mq_flush_lock);
 488
 489         rq_sz = round_up(rq_sz + cmd_size, cache_line_size());
 490         fq->flush_rq = kzalloc_node(rq_sz, flags, node);
 491         if (!fq->flush_rq)
 492                 goto fail_rq;
 493
 494         INIT_LIST_HEAD(&fq->flush_queue[0]);
 495         INIT_LIST_HEAD(&fq->flush_queue[1]);
 496
 497         return fq;
 498
 499  fail_rq:
 500         kfree(fq);
 501  fail:
 502         return NULL;
 503 }
 504
 505 void blk_free_flush_queue(struct blk_flush_queue *fq)
 506 {
 507         /* bio based request queue hasn't flush queue */
 508         if (!fq)
 509                 return;
 510
 511         kfree(fq->flush_rq);
 512         kfree(fq);
 513 }
 514
 515 /*
 516  * Allow driver to set its own lock class to fq->mq_flush_lock for
 517  * avoiding lockdep complaint.
 518  *
 519  * flush_end_io() may be called recursively from some driver, such as
 520  * nvme-loop, so lockdep may complain 'possible recursive locking' because
 521  * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class
 522  * key. We need to assign different lock class for these driver's
 523  * fq->mq_flush_lock for avoiding the lockdep warning.
 524  *
 525  * Use dynamically allocated lock class key for each 'blk_flush_queue'
 526  * instance is over-kill, and more worse it introduces horrible boot delay
 527  * issue because synchronize_rcu() is implied in lockdep_unregister_key which
 528  * is called for each hctx release. SCSI probing may synchronously create and
 529  * destroy lots of MQ request_queues for non-existent devices, and some robot
 530  * test kernel always enable lockdep option. It is observed that more than half
 531  * an hour is taken during SCSI MQ probe with per-fq lock class.
 532  */
 533 void blk_mq_hctx_set_fq_lock_class(struct blk_mq_hw_ctx *hctx,
 534                 struct lock_class_key *key)
 535 {
 536         lockdep_set_class(&hctx->fq->mq_flush_lock, key);
 537 }
 538 EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);