On Mon 27-11-17 11:30:19, Jiang Biao wrote:
> When running ltp stress test for 7*24 hours, the vmscan occasionally
> complains the following warning continuously,
>
> mb_cache_scan+0x0/0x3f0 negative objects to delete
> nr=-9232265467809300450
> ...
>
> The tracing result shows the freeable(mb_cache_count returns)
> is -1, which causes the continuous accumulation and overflow of
> total_scan.
>
> This patch make sure the mb_cache_count not return negative value,
> which make the mbcache shrinker more robust.
>
> Signed-off-by: Jiang Biao <[email protected]>
Going through some old email...
a) c_entry_count is unsigned so your patch is a nop as Coverity properly
noticed.
b) c_entry_count being outside 0..2*cache->c_max_entries is a plain bug. I
went through the logic and cannot find out how that could happen though.
But in either case your patch just does not make sense.
Honza
> ---
> fs/mbcache.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/fs/mbcache.c b/fs/mbcache.c
> index d818fd2..b8b8b9c 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;
> }
>
> --
> 2.7.4
>
--
Jan Kara <[email protected]>
SUSE Labs, CR
