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1// SPDX-License-Identifier: GPL-2.02/*3 * Functions to sequence PREFLUSH and FUA writes.4 *5 * Copyright (C) 2011 Max Planck Institute for Gravitational Physics6 * Copyright (C) 2011 Tejun Heo <tj@kernel.org>7 *8 * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three9 * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request10 * properties and hardware capability.11 *12 * If a request doesn't have data, only REQ_PREFLUSH makes sense, which13 * indicates a simple flush request. If there is data, REQ_PREFLUSH indicates14 * that the device cache should be flushed before the data is executed, and15 * REQ_FUA means that the data must be on non-volatile media on request16 * completion.17 *18 * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any19 * difference. The requests are either completed immediately if there's no data20 * or executed as normal requests otherwise.21 *22 * If the device has writeback cache and supports FUA, REQ_PREFLUSH is23 * 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_PREFLUSH26 * is translated to PREFLUSH and REQ_FUA to POSTFLUSH.27 *28 * The actual execution of flush is double buffered. Whenever a request29 * needs to execute PRE or POSTFLUSH, it queues at30 * fq->flush_queue[fq->flush_pending_idx]. Once certain criteria are met, a31 * REQ_OP_FLUSH is issued and the pending_idx is toggled. When the flush32 * completes, all the requests which were pending are proceeded to the next33 * step. This allows arbitrary merging of different types of PREFLUSH/FUA34 * requests.35 *36 * Currently, the following conditions are used to determine when to issue37 * flush.38 *39 * C1. At any given time, only one flush shall be in progress. This makes40 * 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 shared44 * PREFLUSH.45 *46 * C3. The second condition is ignored if there is a request which has47 * waited longer than FLUSH_PENDING_TIMEOUT. This is to avoid48 * starvation in the unlikely case where there are continuous stream of49 * 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 is56 * complete. The first completion updates the contained bio but doesn't57 * finish it so that the bio submitter is notified only after the whole58 * sequence is complete. This is implemented by testing RQF_FLUSH_SEQ in59 * req_bio_endio().60 *61 * The above peculiarity requires that each PREFLUSH/FUA request has only one62 * bio attached to it, which is guaranteed as they aren't allowed to be63 * 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 */78enum {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 94static void blk_kick_flush(struct request_queue *q,95 struct blk_flush_queue *fq, blk_opf_t flags);96 97static inline struct blk_flush_queue *98blk_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 103static unsigned int blk_flush_cur_seq(struct request *rq)104{105 return 1 << ffz(rq->flush.seq);106}107 108static void blk_flush_restore_request(struct request *rq)109{110 /*111 * After flush data completion, @rq->bio is %NULL but we need to112 * complete the bio again. @rq->biotail is guaranteed to equal the113 * 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 124static 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 sequence137 * @rq: PREFLUSH/FUA request being sequenced138 * @fq: flush queue139 * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero)140 * @error: whether an error occurred141 *142 * @rq just completed @seq part of its flush sequence, record the143 * completion and trigger the next step.144 *145 * CONTEXT:146 * spin_lock_irq(fq->mq_flush_lock)147 */148static 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 else163 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() for185 * flush sequencing and may already have gone through the186 * flush data request completion path. Restore @rq for187 * 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 201static 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 ended222 * because its .end_io() is called from timeout code path too for223 * 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 257bool 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 request264 * @q: request_queue being kicked265 * @fq: flush queue266 * @flags: cmd_flags of the original request267 *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 */275static 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_idx295 * 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 request303 * since they can't be in flight at the same time. And acquire304 * the tag's ownership for flush req.305 *306 * In case of IO scheduler, flush rq need to borrow scheduler tag307 * 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 else315 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 one323 * implied in refcount_inc_not_zero() called from324 * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref325 * and READ flush_rq->end_io326 */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 337static 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. Read353 * 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 to359 * 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 369static 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 */382bool 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. Adjust407 * 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 any415 * of those flags, we have to set REQ_SYNC to avoid skewing416 * 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 may424 * translate into nothing if the underlying device does not425 * advertise a write-back cache. In this case, simply426 * 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 can433 * 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 trigger440 * 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 it451 * 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 flush463 * @bdev: blockdev to issue flush for464 *465 * Description:466 * Issue a flush for the block device in question.467 */468int 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}475EXPORT_SYMBOL(blkdev_issue_flush);476 477struct 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 505void 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 for517 * avoiding lockdep complaint.518 *519 * flush_end_io() may be called recursively from some driver, such as520 * nvme-loop, so lockdep may complain 'possible recursive locking' because521 * all 'struct blk_flush_queue' instance share same mq_flush_lock lock class522 * key. We need to assign different lock class for these driver's523 * 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 delay527 * issue because synchronize_rcu() is implied in lockdep_unregister_key which528 * is called for each hctx release. SCSI probing may synchronously create and529 * destroy lots of MQ request_queues for non-existent devices, and some robot530 * test kernel always enable lockdep option. It is observed that more than half531 * an hour is taken during SCSI MQ probe with per-fq lock class.532 */533void 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}538EXPORT_SYMBOL_GPL(blk_mq_hctx_set_fq_lock_class);539