From: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
To: mhocko@kernel.org
Cc: akpm@linux-foundation.org, andrea@kernel.org,
kirill@shutemov.name, oleg@redhat.com,
wenwei.tww@alibaba-inc.com, linux-mm@kvack.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer
Date: Sat, 12 Aug 2017 00:46:18 +0900 [thread overview]
Message-ID: <201708120046.AFI81780.OHMFtFSOFVQJOL@I-love.SAKURA.ne.jp> (raw)
In-Reply-To: <20170811120825.GG30811@dhcp22.suse.cz>
Michal Hocko wrote:
> On Fri 11-08-17 16:54:36, Tetsuo Handa wrote:
> > Michal Hocko wrote:
> > > On Fri 11-08-17 11:28:52, Tetsuo Handa wrote:
> > > > Will you explain the mechanism why random values are written instead of zeros
> > > > so that this patch can actually fix the race problem?
> > >
> > > I am not sure what you mean here. Were you able to see a write with an
> > > unexpected content?
> >
> > Yes. See http://lkml.kernel.org/r/201708072228.FAJ09347.tOOVOFFQJSHMFL@I-love.SAKURA.ne.jp .
>
> Ahh, I've missed that random part of your output. That is really strange
> because AFAICS the oom reaper shouldn't really interact here. We are
> only unmapping anonymous memory and even if a refault slips through we
> should always get zeros.
>
> Your test case doesn't mmap MAP_PRIVATE of a file so we shouldn't even
> get any uninitialized data from a file by missing CoWed content. The
> only possible explanations would be that a page fault returned a
> non-zero data which would be a bug on its own or that a file write
> extend the file without actually writing to it which smells like a fs
> bug to me.
As I wrote at http://lkml.kernel.org/r/201708112053.FIG52141.tHJSOQFLOFMFOV@I-love.SAKURA.ne.jp ,
I don't think it is a fs bug.
>
> Anyway I wasn't able to reproduce this and I was running your usecase
> in the loop for quite some time (with xfs storage). How reproducible
> is this? If you can reproduce easily can you simply comment out
> unmap_page_range in __oom_reap_task_mm and see if that makes any change
> just to be sure that the oom reaper can be ruled out?
Frequency of writing not-zero values is lower than frequency of writing zero values.
But if I comment out unmap_page_range() in __oom_reap_task_mm(), I can't even
reproduce writing zero values. As far as I tested, writing not-zero values occurs
only if the OOM reaper is involved.
next prev parent reply other threads:[~2017-08-11 15:46 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-07 11:38 [PATCH 0/2] mm, oom: fix oom_reaper fallouts Michal Hocko
2017-08-07 11:38 ` [PATCH 1/2] mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS Michal Hocko
2017-08-15 0:49 ` David Rientjes
2017-08-07 11:38 ` [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer Michal Hocko
2017-08-08 17:48 ` Andrea Arcangeli
2017-08-08 23:35 ` Tetsuo Handa
2017-08-09 18:36 ` Andrea Arcangeli
2017-08-10 8:21 ` Michal Hocko
2017-08-10 13:33 ` Michal Hocko
2017-08-11 2:28 ` Tetsuo Handa
2017-08-11 7:09 ` Michal Hocko
2017-08-11 7:54 ` Tetsuo Handa
2017-08-11 10:22 ` Andrea Arcangeli
2017-08-11 10:42 ` Andrea Arcangeli
2017-08-11 11:53 ` Tetsuo Handa
2017-08-11 12:08 ` Michal Hocko
2017-08-11 15:46 ` Tetsuo Handa [this message]
2017-08-14 13:59 ` Michal Hocko
[not found] ` <201708142251.v7EMp3j9081456@www262.sakura.ne.jp>
2017-08-15 6:55 ` Michal Hocko
2017-08-15 8:41 ` Michal Hocko
[not found] ` <201708151006.v7FA6SxD079619@www262.sakura.ne.jp>
2017-08-15 12:26 ` Michal Hocko
[not found] ` <201708151258.v7FCwTsV029946@www262.sakura.ne.jp>
2017-08-17 13:58 ` Michal Hocko
2017-08-07 13:28 ` [PATCH 0/2] mm, oom: fix oom_reaper fallouts Tetsuo Handa
2017-08-07 14:04 ` Michal Hocko
2017-08-07 15:23 ` Tetsuo Handa
2017-08-15 12:29 ` Michal Hocko
-- strict thread matches above, loose matches on Subject: below --
2017-08-04 8:32 Re: [PATCH] mm, oom: fix potential data corruption when oom_reaper races with writer Michal Hocko
2017-08-04 8:33 ` [PATCH 1/2] mm: fix double mmap_sem unlock on MMF_UNSTABLE enforced SIGBUS Michal Hocko
2017-08-04 8:33 ` [PATCH 2/2] mm, oom: fix potential data corruption when oom_reaper races with writer Michal Hocko
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