Re: low-memory crash with patch "capture a page under direct compaction"

[Mel Gorman <mgorman@techsingularity.net>]

On Mon, Mar 04, 2019 at 10:55:04PM -0500, Qian Cai wrote:
> Reverted the patches below from linux-next seems fixed a crash while running LTP
> oom01.
> 
> 915c005358c1 mm, compaction: Capture a page under direct compaction -fix
> e492a5711b67 mm, compaction: capture a page under direct compaction
> 
> Especially, just removed this chunk along seems fixed the problem.
> 
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -2227,10 +2227,10 @@ compact_zone(struct compact_control *cc, struct
> capture_control *capc)
>                 }
> 
>                 /* Stop if a page has been captured */
> -               if (capc && capc->page) {
> -                       ret = COMPACT_SUCCESS;
> -                       break;
> -               }
> 

It's hard to make sense of how this is connected to the bug. The
out-of-bounds warning would have required page flags to be corrupted
quite badly or maybe the use of an uninitialised page. How reproducible
has this been for you? I just ran the test 100 times with UBSAN and page
alloc debugging enabled and it completed correctly.

-- 
Mel Gorman
SUSE Labs