// SPDX-License-Identifier: GPL-2.0/* * Functions to sequence PREFLUSH and FUA writes. * * Copyright (C) 2011		Max Planck Institute for Gravitational Physics * Copyright (C) 2011		Tejun Heo <tj@kernel.org> * * REQ_{PREFLUSH|FUA} requests are decomposed to sequences consisted of three * optional steps - PREFLUSH, DATA and POSTFLUSH - according to the request * properties and hardware capability. * * If a request doesn't have data, only REQ_PREFLUSH makes sense, which * indicates a simple flush request.  If there is data, REQ_PREFLUSH indicates * that the device cache should be flushed before the data is executed, and * REQ_FUA means that the data must be on non-volatile media on request * completion. * * If the device doesn't have writeback cache, PREFLUSH and FUA don't make any * difference.  The requests are either completed immediately if there's no data * or executed as normal requests otherwise. * * If the device has writeback cache and supports FUA, REQ_PREFLUSH is * translated to PREFLUSH but REQ_FUA is passed down directly with DATA. * * If the device has writeback cache and doesn't support FUA, REQ_PREFLUSH * is translated to PREFLUSH and REQ_FUA to POSTFLUSH. * * The actual execution of flush is double buffered.  Whenever a request * needs to execute PRE or POSTFLUSH, it queues at * fq->flush_queue[fq->flush_pending_idx].  Once certain criteria are met, a * REQ_OP_FLUSH is issued and the pending_idx is toggled.  When the flush * completes, all the requests which were pending are proceeded to the next * step.  This allows arbitrary merging of different types of PREFLUSH/FUA * requests. * * Currently, the following conditions are used to determine when to issue * flush. * * C1. At any given time, only one flush shall be in progress.  This makes *     double buffering sufficient. * * C2. Flush is deferred if any request is executing DATA of its sequence. *     This avoids issuing separate POSTFLUSHes for requests which shared *     PREFLUSH. * * C3. The second condition is ignored if there is a request which has *     waited longer than FLUSH_PENDING_TIMEOUT.  This is to avoid *     starvation in the unlikely case where there are continuous stream of *     FUA (without PREFLUSH) requests. * * For devices which support FUA, it isn't clear whether C2 (and thus C3) * is beneficial. * * Note that a sequenced PREFLUSH/FUA request with DATA is completed twice. * Once while executing DATA and again after the whole sequence is * complete.  The first completion updates the contained bio but doesn't * finish it so that the bio submitter is notified only after the whole * sequence is complete.  This is implemented by testing RQF_FLUSH_SEQ in * req_bio_endio(). * * The above peculiarity requires that each PREFLUSH/FUA request has only one * bio attached to it, which is guaranteed as they aren't allowed to be * merged in the usual way. */ #include <linux/kernel.h>#include <linux/module.h>#include <linux/bio.h>#include <linux/blkdev.h>#include <linux/gfp.h>#include <linux/part_stat.h> #include "blk.h"#include "blk-mq.h"#include "blk-mq-sched.h" /* PREFLUSH/FUA sequences */enum {	REQ_FSEQ_PREFLUSH	= (1 << 0), /* pre-flushing in progress */	REQ_FSEQ_DATA		= (1 << 1), /* data write in progress */	REQ_FSEQ_POSTFLUSH	= (1 << 2), /* post-flushing in progress */	REQ_FSEQ_DONE		= (1 << 3), 	REQ_FSEQ_ACTIONS	= REQ_FSEQ_PREFLUSH | REQ_FSEQ_DATA |				  REQ_FSEQ_POSTFLUSH, 	/*	 * If flush has been pending longer than the following timeout,	 * it's issued even if flush_data requests are still in flight.	 */	FLUSH_PENDING_TIMEOUT	= 5 * HZ,}; static void blk_kick_flush(struct request_queue *q,			   struct blk_flush_queue *fq, blk_opf_t flags); static inline struct blk_flush_queue *blk_get_flush_queue(struct blk_mq_ctx *ctx){	return blk_mq_map_queue(REQ_OP_FLUSH, ctx)->fq;} static unsigned int blk_flush_cur_seq(struct request *rq){	return 1 << ffz(rq->flush.seq);} static void blk_flush_restore_request(struct request *rq){	/*	 * After flush data completion, @rq->bio is %NULL but we need to	 * complete the bio again.  @rq->biotail is guaranteed to equal the	 * original @rq->bio.  Restore it.	 */	rq->bio = rq->biotail;	if (rq->bio)		rq->__sector = rq->bio->bi_iter.bi_sector; 	/* make @rq a normal request */	rq->rq_flags &= ~RQF_FLUSH_SEQ;	rq->end_io = rq->flush.saved_end_io;} static void blk_account_io_flush(struct request *rq){	struct block_device *part = rq->q->disk->part0; 	part_stat_lock();	part_stat_inc(part, ios[STAT_FLUSH]);	part_stat_add(part, nsecs[STAT_FLUSH],		      blk_time_get_ns() - rq->start_time_ns);	part_stat_unlock();} /** * blk_flush_complete_seq - complete flush sequence * @rq: PREFLUSH/FUA request being sequenced * @fq: flush queue * @seq: sequences to complete (mask of %REQ_FSEQ_*, can be zero) * @error: whether an error occurred * * @rq just completed @seq part of its flush sequence, record the * completion and trigger the next step. * * CONTEXT: * spin_lock_irq(fq->mq_flush_lock) */static void blk_flush_complete_seq(struct request *rq,				   struct blk_flush_queue *fq,				   unsigned int seq, blk_status_t error){	struct request_queue *q = rq->q;	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];	blk_opf_t cmd_flags; 	BUG_ON(rq->flush.seq & seq);	rq->flush.seq |= seq;	cmd_flags = rq->cmd_flags; 	if (likely(!error))		seq = blk_flush_cur_seq(rq);	else		seq = REQ_FSEQ_DONE; 	switch (seq) {	case REQ_FSEQ_PREFLUSH:	case REQ_FSEQ_POSTFLUSH:		/* queue for flush */		if (list_empty(pending))			fq->flush_pending_since = jiffies;		list_add_tail(&rq->queuelist, pending);		break; 	case REQ_FSEQ_DATA:		fq->flush_data_in_flight++;		spin_lock(&q->requeue_lock);		list_move(&rq->queuelist, &q->requeue_list);		spin_unlock(&q->requeue_lock);		blk_mq_kick_requeue_list(q);		break; 	case REQ_FSEQ_DONE:		/*		 * @rq was previously adjusted by blk_insert_flush() for		 * flush sequencing and may already have gone through the		 * flush data request completion path.  Restore @rq for		 * normal completion and end it.		 */		list_del_init(&rq->queuelist);		blk_flush_restore_request(rq);		blk_mq_end_request(rq, error);		break; 	default:		BUG();	} 	blk_kick_flush(q, fq, cmd_flags);} static enum rq_end_io_ret flush_end_io(struct request *flush_rq,				       blk_status_t error,				       const struct io_comp_batch *iob){	struct request_queue *q = flush_rq->q;	struct list_head *running;	struct request *rq, *n;	unsigned long flags = 0;	struct blk_flush_queue *fq = blk_get_flush_queue(flush_rq->mq_ctx); 	/* release the tag's ownership to the req cloned from */	spin_lock_irqsave(&fq->mq_flush_lock, flags); 	if (!req_ref_put_and_test(flush_rq)) {		fq->rq_status = error;		spin_unlock_irqrestore(&fq->mq_flush_lock, flags);		return RQ_END_IO_NONE;	} 	blk_account_io_flush(flush_rq);	/*	 * Flush request has to be marked as IDLE when it is really ended	 * because its .end_io() is called from timeout code path too for	 * avoiding use-after-free.	 */	WRITE_ONCE(flush_rq->state, MQ_RQ_IDLE);	if (fq->rq_status != BLK_STS_OK) {		error = fq->rq_status;		fq->rq_status = BLK_STS_OK;	} 	if (!q->elevator) {		flush_rq->tag = BLK_MQ_NO_TAG;	} else {		blk_mq_put_driver_tag(flush_rq);		flush_rq->internal_tag = BLK_MQ_NO_TAG;	} 	running = &fq->flush_queue[fq->flush_running_idx];	BUG_ON(fq->flush_pending_idx == fq->flush_running_idx); 	/* account completion of the flush request */	fq->flush_running_idx ^= 1; 	/* and push the waiting requests to the next stage */	list_for_each_entry_safe(rq, n, running, queuelist) {		unsigned int seq = blk_flush_cur_seq(rq); 		BUG_ON(seq != REQ_FSEQ_PREFLUSH && seq != REQ_FSEQ_POSTFLUSH);		list_del_init(&rq->queuelist);		blk_flush_complete_seq(rq, fq, seq, error);	} 	spin_unlock_irqrestore(&fq->mq_flush_lock, flags);	return RQ_END_IO_NONE;} bool is_flush_rq(struct request *rq){	return rq->end_io == flush_end_io;} /** * blk_kick_flush - consider issuing flush request * @q: request_queue being kicked * @fq: flush queue * @flags: cmd_flags of the original request * * Flush related states of @q have changed, consider issuing flush request. * Please read the comment at the top of this file for more info. * * CONTEXT: * spin_lock_irq(fq->mq_flush_lock) * */static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,			   blk_opf_t flags){	struct list_head *pending = &fq->flush_queue[fq->flush_pending_idx];	struct request *first_rq =		list_first_entry(pending, struct request, queuelist);	struct request *flush_rq = fq->flush_rq; 	/* C1 described at the top of this file */	if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))		return; 	/* C2 and C3 */	if (fq->flush_data_in_flight &&	    time_before(jiffies,			fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))		return; 	/*	 * Issue flush and toggle pending_idx.  This makes pending_idx	 * different from running_idx, which means flush is in flight.	 */	fq->flush_pending_idx ^= 1; 	blk_rq_init(q, flush_rq); 	/*	 * In case of none scheduler, borrow tag from the first request	 * since they can't be in flight at the same time. And acquire	 * the tag's ownership for flush req.	 *	 * In case of IO scheduler, flush rq need to borrow scheduler tag	 * just for cheating put/get driver tag.	 */	flush_rq->mq_ctx = first_rq->mq_ctx;	flush_rq->mq_hctx = first_rq->mq_hctx; 	if (!q->elevator)		flush_rq->tag = first_rq->tag;	else		flush_rq->internal_tag = first_rq->internal_tag; 	flush_rq->cmd_flags = REQ_OP_FLUSH | REQ_PREFLUSH;	flush_rq->cmd_flags |= (flags & REQ_DRV) | (flags & REQ_FAILFAST_MASK);	flush_rq->rq_flags |= RQF_FLUSH_SEQ;	flush_rq->end_io = flush_end_io;	/*	 * Order WRITE ->end_io and WRITE rq->ref, and its pair is the one	 * implied in refcount_inc_not_zero() called from	 * blk_mq_find_and_get_req(), which orders WRITE/READ flush_rq->ref	 * and READ flush_rq->end_io	 */	smp_wmb();	req_ref_set(flush_rq, 1); 	spin_lock(&q->requeue_lock);	list_add_tail(&flush_rq->queuelist, &q->flush_list);	spin_unlock(&q->requeue_lock); 	blk_mq_kick_requeue_list(q);} static enum rq_end_io_ret mq_flush_data_end_io(struct request *rq,					       blk_status_t error,					       const struct io_comp_batch *iob){	struct request_queue *q = rq->q;	struct blk_mq_hw_ctx *hctx = rq->mq_hctx;	struct blk_mq_ctx *ctx = rq->mq_ctx;	unsigned long flags;	struct blk_flush_queue *fq = blk_get_flush_queue(ctx); 	if (q->elevator) {		WARN_ON(rq->tag < 0);		blk_mq_put_driver_tag(rq);	} 	/*	 * After populating an empty queue, kick it to avoid stall.  Read	 * the comment in flush_end_io().	 */	spin_lock_irqsave(&fq->mq_flush_lock, flags);	fq->flush_data_in_flight--;	/*	 * May have been corrupted by rq->rq_next reuse, we need to	 * re-initialize rq->queuelist before reusing it here.	 */	INIT_LIST_HEAD(&rq->queuelist);	blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);	spin_unlock_irqrestore(&fq->mq_flush_lock, flags); 	blk_mq_sched_restart(hctx);	return RQ_END_IO_NONE;} static void blk_rq_init_flush(struct request *rq){	rq->flush.seq = 0;	rq->rq_flags |= RQF_FLUSH_SEQ;	rq->flush.saved_end_io = rq->end_io; /* Usually NULL */	rq->end_io = mq_flush_data_end_io;} /* * Insert a PREFLUSH/FUA request into the flush state machine. * Returns true if the request has been consumed by the flush state machine, * or false if the caller should continue to process it. */bool blk_insert_flush(struct request *rq){	struct request_queue *q = rq->q;	struct blk_flush_queue *fq = blk_get_flush_queue(rq->mq_ctx);	bool supports_fua = q->limits.features & BLK_FEAT_FUA;	unsigned int policy = 0; 	/* FLUSH/FUA request must never be merged */	WARN_ON_ONCE(rq->bio != rq->biotail); 	if (blk_rq_sectors(rq))		policy |= REQ_FSEQ_DATA; 	/*	 * Check which flushes we need to sequence for this operation.	 */	if (blk_queue_write_cache(q)) {		if (rq->cmd_flags & REQ_PREFLUSH)			policy |= REQ_FSEQ_PREFLUSH;		if ((rq->cmd_flags & REQ_FUA) && !supports_fua)			policy |= REQ_FSEQ_POSTFLUSH;	} 	/*	 * @policy now records what operations need to be done.  Adjust	 * REQ_PREFLUSH and FUA for the driver.	 */	rq->cmd_flags &= ~REQ_PREFLUSH;	if (!supports_fua)		rq->cmd_flags &= ~REQ_FUA; 	/*	 * REQ_PREFLUSH|REQ_FUA implies REQ_SYNC, so if we clear any	 * of those flags, we have to set REQ_SYNC to avoid skewing	 * the request accounting.	 */	rq->cmd_flags |= REQ_SYNC; 	switch (policy) {	case 0:		/*		 * An empty flush handed down from a stacking driver may		 * translate into nothing if the underlying device does not		 * advertise a write-back cache.  In this case, simply		 * complete the request.		 */		blk_mq_end_request(rq, 0);		return true;	case REQ_FSEQ_DATA:		/*		 * If there's data, but no flush is necessary, the request can		 * be processed directly without going through flush machinery.		 * Queue for normal execution.		 */		return false;	case REQ_FSEQ_DATA | REQ_FSEQ_POSTFLUSH:		/*		 * Initialize the flush fields and completion handler to trigger		 * the post flush, and then just pass the command on.		 */		blk_rq_init_flush(rq);		rq->flush.seq |= REQ_FSEQ_PREFLUSH;		spin_lock_irq(&fq->mq_flush_lock);		fq->flush_data_in_flight++;		spin_unlock_irq(&fq->mq_flush_lock);		return false;	default:		/*		 * Mark the request as part of a flush sequence and submit it		 * for further processing to the flush state machine.		 */		blk_rq_init_flush(rq);		spin_lock_irq(&fq->mq_flush_lock);		blk_flush_complete_seq(rq, fq, REQ_FSEQ_ACTIONS & ~policy, 0);		spin_unlock_irq(&fq->mq_flush_lock);		return true;	}} /** * blkdev_issue_flush - queue a flush * @bdev:	blockdev to issue flush for * * Description: *    Issue a flush for the block device in question. */int blkdev_issue_flush(struct block_device *bdev){	struct bio bio; 	bio_init(&bio, bdev, NULL, 0, REQ_OP_WRITE | REQ_PREFLUSH);	return submit_bio_wait(&bio);}EXPORT_SYMBOL(blkdev_issue_flush); struct blk_flush_queue *blk_alloc_flush_queue(int node, int cmd_size,					      gfp_t flags){	struct blk_flush_queue *fq;	int rq_sz = sizeof(struct request); 	fq = kzalloc_node(sizeof(*fq), flags, node);	if (!fq)		goto fail; 	spin_lock_init(&fq->mq_flush_lock); 	rq_sz = round_up(rq_sz + cmd_size, cache_line_size());	fq->flush_rq = kzalloc_node(rq_sz, flags, node);	if (!fq->flush_rq)		goto fail_rq; 	INIT_LIST_HEAD(&fq->flush_queue[0]);	INIT_LIST_HEAD(&fq->flush_queue[1]); 	return fq; 

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