linux-kernel - Re: Processes hang in an unkillable state

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Message-ID: <BANLkTikoDELrA-RtA9BLm64mfoPgdADR0Q@mail.gmail.com>
Date:	Tue, 12 Apr 2011 13:22:39 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Robert Święcki <robert@...ecki.net>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Américo Wang <xiyou.wangcong@...il.com>,
	linux-kernel@...r.kernel.org, Hugh Dickins <hughd@...gle.com>,
	Miklos Szeredi <mszeredi@...e.cz>
Subject: Re: Processes hang in an unkillable state

On Tue, Apr 12, 2011 at 1:03 PM, Robert Święcki <robert@...ecki.net> wrote:
>>
>> Ok, applied Linus' patch and got the following (kdb dump in the attachment):
>>
>> It contains references to sys_mlock, but in another process/user that
>> oopsed (there are iknowthis and iknowthis2 processes running under
>> test and test2 users). I think I'll simply disable sys_madvise in the
>> fuzzer; and treat this oops as a separate issue.

This does seem to be something else.

It looks like some kind of live-lock situation between two processes
both doing madvise() and causing vmtruncate_range() calls.

Miklos wrote this patch for something bad in this area to serialize
concurrent unmap_mapping_range() calls in order to not restart forever
on vm_truncate_count. That got merged into 2.6.38, so it's there, but
I wonder if there is some case it misses.

                           Linus
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