linux-kernel - Re: [PATCH AUTOSEL for 4.9 38/55] fs/mbcache.c: make count

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Date:   Tue, 23 Jan 2018 20:29:20 -0800
From:   Eric Biggers <ebiggers3@...il.com>
To:     Sasha Levin <Alexander.Levin@...rosoft.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jiang Biao <jiang.biao2@....com.cn>,
        Al Viro <viro@...iv.linux.org.uk>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...nel.org>,
        "zhong.weidong@....com.cn" <zhong.weidong@....com.cn>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH AUTOSEL for 4.9 38/55] fs/mbcache.c: make count_objects()
 more robust

On Wed, Jan 24, 2018 at 04:15:49AM +0000, Sasha Levin wrote:
> From: Jiang Biao <jiang.biao2@....com.cn>
> 
> [ 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@zte.com.cn
> Signed-off-by: Jiang Biao <jiang.biao2@....com.cn>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Michal Hocko <mhocko@...nel.org>
> Cc: <zhong.weidong@....com.cn>
> Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
> ---
>  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?