linux-kernel - [PATCH 3.16 068/305] bcache: fix wrong cache

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Message-ID: <lsq.1549201508.277992422@decadent.org.uk>
Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jens Axboe" <axboe@...nel.dk>, "Coly Li" <colyli@...e.de>,
        "tang.junhui" <tang.junhui@....com.cn>,
        "Michael Lyle" <mlyle@...e.org>
Subject: [PATCH 3.16 068/305] bcache: fix wrong cache_misses statistics

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: "tang.junhui" <tang.junhui@....com.cn>

commit c157313791a999646901b3e3c6888514ebc36d62 upstream.

Currently, Cache missed IOs are identified by s->cache_miss, but actually,
there are many situations that missed IOs are not assigned a value for
s->cache_miss in cached_dev_cache_miss(), for example, a bypassed IO
(s->iop.bypass = 1), or the cache_bio allocate failed. In these situations,
it will go to out_put or out_submit, and s->cache_miss is null, which leads
bch_mark_cache_accounting() to treat this IO as a hit IO.

[ML: applied by 3-way merge]

Signed-off-by: tang.junhui <tang.junhui@....com.cn>
Reviewed-by: Michael Lyle <mlyle@...e.org>
Reviewed-by: Coly Li <colyli@...e.de>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/md/bcache/request.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -462,6 +462,7 @@ struct search {
 	unsigned		recoverable:1;
 	unsigned		write:1;
 	unsigned		read_dirty_data:1;
+	unsigned		cache_missed:1;
 
 	unsigned long		start_time;
 
@@ -651,6 +652,7 @@ static inline struct search *search_allo
 
 	s->orig_bio		= bio;
 	s->cache_miss		= NULL;
+	s->cache_missed		= 0;
 	s->d			= d;
 	s->recoverable		= 1;
 	s->write		= (bio->bi_rw & REQ_WRITE) != 0;
@@ -774,7 +776,7 @@ static void cached_dev_read_done_bh(stru
 	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
 
 	bch_mark_cache_accounting(s->iop.c, s->d,
-				  !s->cache_miss, s->iop.bypass);
+				  !s->cache_missed, s->iop.bypass);
 	trace_bcache_read(s->orig_bio, !s->cache_miss, s->iop.bypass);
 
 	if (s->iop.error)
@@ -793,6 +795,8 @@ static int cached_dev_cache_miss(struct
 	struct cached_dev *dc = container_of(s->d, struct cached_dev, disk);
 	struct bio *miss, *cache_bio;
 
+	s->cache_missed = 1;
+
 	if (s->cache_miss || s->iop.bypass) {
 		miss = bio_next_split(bio, sectors, GFP_NOIO, s->d->bio_split);
 		ret = miss == bio ? MAP_DONE : MAP_CONTINUE;