Re: [PATCH AUTOSEL for 4.9 38/55] fs/mbcache.c: make count_objects() more robust

[Eric Biggers]

On Wed, Jan 24, 2018 at 04:15:49AM +0000, Sasha Levin wrote:
> From: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> 
> [ Upstream commit d5dabd633922ac5ee5bcc67748f7defb8b211469 ]
> 
> When running ltp stress test for 7*24 hours, vmscan occasionally emits
> the following warning continuously:
> 
>   mb_cache_scan+0x0/0x3f0 negative objects to delete
>   nr=-9232265467809300450
>   ...
> 
> Tracing shows the freeable(mb_cache_count returns) is -1, which causes
> the continuous accumulation and overflow of total_scan.
> 
> This patch makes sure that mb_cache_count() cannot return a negative
> value, which makes the mbcache shrinker more robust.
> 
> Link: http://lkml.kernel.org/r/1511753419-52328-1-git-send-email-jiang.biao2@xxxxxxxxxx
> Signed-off-by: Jiang Biao <jiang.biao2@xxxxxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Minchan Kim <minchan@xxxxxxxxxx>
> Cc: Michal Hocko <mhocko@xxxxxxxxxx>
> Cc: <zhong.weidong@xxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
> ---
>  fs/mbcache.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/mbcache.c b/fs/mbcache.c
> index c5bd19ffa326..35ab4187bfe1 100644
> --- a/fs/mbcache.c
> +++ b/fs/mbcache.c
> @@ -269,6 +269,9 @@ static unsigned long mb_cache_count(struct shrinker *shrink,
>  	struct mb_cache *cache = container_of(shrink, struct mb_cache,
>  					      c_shrink);
>  
> +	/* Unlikely, but not impossible */
> +	if (unlikely(cache->c_entry_count < 0))
> +		return 0;
>  	return cache->c_entry_count;
>  }

This patch is broken and is reverted in linux-next, via ext4/dev:

bbe45d2460da ("mbcache: revert "fs/mbcache.c: make count_objects() more robust"")

Can you please update your "autosel" script/process/whatever to not select
commits that are reverted?