From: Christoph Hellwig <hch@lst.de>
Date: Tue, 8 Mar 2022 06:51:47 +0100
Subject: [PATCH] blk-mq: do not include passthrough requests in I/O accounting
Git-commit: 41fa722239b46f0c033da94746212344175cdaa0
Patch-mainline: v5.18-rc1
References: jsc#PED-1183

I/O accounting buckets I/O into the read/write/discard categories into
which passthrough I/O does not fit at all.  It also accounts to the
block_device, which may not even exist for passthrough I/O.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
Link: https://lore.kernel.org/r/20220308055200.735835-2-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Acked-by: Hannes Reinecke <hare@suse.com>
---
 block/blk-mq.c | 11 ++++++++---
 block/blk.h    |  2 +-
 2 files changed, 9 insertions(+), 4 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index e8d6d7a05a43..40f634ab7026 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -884,10 +884,15 @@ static inline void blk_account_io_done(struct request *req, u64 now)
 
 static void __blk_account_io_start(struct request *rq)
 {
-	/* passthrough requests can hold bios that do not have ->bi_bdev set */
-	if (rq->bio && rq->bio->bi_bdev)
+	/*
+	 * All non-passthrough requests are created from a bio with one
+	 * exception: when a flush command that is part of a flush sequence
+	 * generated by the state machine in blk-flush.c is cloned onto the
+	 * lower device by dm-multipath we can get here without a bio.
+	 */
+	if (rq->bio)
 		rq->part = rq->bio->bi_bdev;
-	else if (rq->q->disk)
+	else
 		rq->part = rq->q->disk->part0;
 
 	part_stat_lock();
diff --git a/block/blk.h b/block/blk.h
index ebaa59ca46ca..6f21859c7f0f 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -325,7 +325,7 @@ int blk_dev_init(void);
  */
 static inline bool blk_do_io_stat(struct request *rq)
 {
-	return (rq->rq_flags & RQF_IO_STAT) && rq->q->disk;
+	return (rq->rq_flags & RQF_IO_STAT) && !blk_rq_is_passthrough(rq);
 }
 
 void update_io_ticks(struct block_device *part, unsigned long now, bool end);
-- 
2.35.3