linux-kernel - Re: [PATCH] mm: fix possible cause of a page

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Message-ID: <BANLkTik0oYcwtN5jzs4rfHfDyNUMYJdqhg@mail.gmail.com>
Date:	Tue, 12 Apr 2011 18:17:45 +0200
From:	Robert Święcki <robert@...ecki.net>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Michel Lespinasse <walken@...gle.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>
Subject: Re: [PATCH] mm: fix possible cause of a page_mapped BUG

>>> So, if this case is not caught later on in the code, I guess it solves
>>> the problem. During the fuzzing I didn't experience any panic's, but
>>> some other problems arose, i.e. cannot read /proc/<pid>/maps for some
>>> processes (sys_read hangs, and such process cannot be killed or
>>> stopped with any signal, still it's running (R state) and using CPU -
>>> I'll submit another report for that).
>>
>> Hmm. Sounds like an endless loop in kernel mode.
>>
>> Use "perf record -ag" as root, it should show up very clearly in the report.
>>
>>                          Linus
>
> I've put some data here -
> http://groups.google.com/group/fa.linux.kernel/browse_thread/thread/4345dcc4f7750ce2
> - I think it's somewhat connected (sys_mlock appears on both cases).
>
> Attaching perf data (for 2.6.38) + kdb dumpall + procdump for process 14158
>
> Those 3 processes cannot be stopped/killed
>
> 14158 66.2  0.0   8380  3012 ?  RL  /tmp/iknowthis
> 17100 63.6  0.1  18248  4004 ?  RL  /tmp/iknowthis
> 19772 63.8  0.0   4000  1888 ?   RL  /tmp/iknowthis

Also, the system doesn't look usable after such fuzzing (executing a
few times some pretty deterministic program)

root@...-test:~# gcc -m32 mlock.c  -o mlock

root@...-test:~# ./mlock
./mlock: relocation error: ./mlock: symbol perror, version GLIBC_2.0
not defined in file libc.so.6 with link time reference

root@...-test:~# ./mlock
mmap: Success
RET: 0xf751f000
mremap: Invalid argument
RET: 0xffffffff

root@...-test:~# ./mlock
Segmentation fault

root@...-test:~# dmesg | tail -n 1
[ 5164.961568] mlock[7097]: segfault at 0 ip           (null) sp
00000000ff8a00d4 error 14 in mlock[8048000+1000]

-- 
Robert Święcki
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