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

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Message-ID: <BANLkTikbsxDD5shY+9GxWSMSv=G2NfBFAw@mail.gmail.com>
Date:	Wed, 13 Apr 2011 14:19:10 +0200
From:	Robert Święcki <robert@...ecki.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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 Wed, Apr 13, 2011 at 12:43 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>> btw, here might be another path which hits this (at least I think so).
>
> So both mprotect and mlock will do the same "split/merge vma's as
> necessary", but neither of them should actually ever _expand_ a
> mapping or change the vm_pgoff of a vma (except to fix up the pgoff as
> a vma is split).
>
> So what I think is happening is that a previous vma operation (like
> the mremap or the stack expansion) did the expand and created a vma
> with a wrapping vm_pgoff. But nothing bad happened, because nobody
> really _cares_ about the wrapping until later, when we split the vma.
>
> So I think (and hope) that your mprotect issue is exactly the same as
> your mlock issue, and that the deeper problem was the earlier stack
> expansion.

So, after ~12h of testing I don't see any crashes. Currently, I'm
testing with 2.6.39-rc3 with 2 of your patches applied (1st patching
mlock.c/memory.c, 2nd: mmap.c).

It's still crashing with sys_madvise (as reported earlier), and I'm
going to re-enable all syscalls now (madvise, getdents(64), readdir),
which were disabled before. If something unrelated to the problems
discussed in this thread happens, I'll report it in another thread.

-- 
Robert Święcki
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