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References: <20090614081052.GA9276@elte.hu> <4A34B2E2.7080702@cs.helsinki.fi>
	 <84144f020906140130w189239c0l56dccad99529aa7@mail.gmail.com>
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Date: Mon, 15 Jun 2009 01:03:01 +0200
Message-ID: <19f34abd0906141603o2edadf22h2d61408b9abdb7a3@mail.gmail.com>
Subject: Re: tty_ldisc_try_get(): BUG kmalloc-8: Poison overwritten
From: Vegard Nossum <vegard.nossum@gmail.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Ingo Molnar <mingo@elte.hu>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       linux-kernel@vger.kernel.org, "Rafael J. Wysocki" <rjw@sisk.pl>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>
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2009/6/14 Pekka Enberg <penberg@cs.helsinki.fi>:
> On Sun, Jun 14, 2009 at 11:20 AM, Pekka Enberg<penberg@cs.helsinki.fi> wrote:
>>> You could add something like
>>>
>>>  WARN_ON(ld->refcount == 0x6b)
>>>
>>> to tty_ldisc_deref() to see if that triggers.
>
> On Sun, Jun 14, 2009 at 11:30 AM, Pekka Enberg<penberg@cs.helsinki.fi> wrote:
>> Make that
>>
>>    WARN_ON(ld->refcount == (int)0xa56b6b6b)
>>
>> instead.
>
> And oh, kmemcheck should be able to catch this too. :-)
>

I was able to get this trace:

(none) login: [  867.947401] WARNING: kmemcheck: Caught 32-bit read
from freed memory (469e2f44)
[  867.962162] 00000000020000000038bf41020000000038bf41020000000038bf4102000000
[  868.012078]  i i i i f f f f i i i i i i i i i i i i i i i i i i i i i i i i
[  868.061629]          ^
[  868.067686]
[  868.071709] Pid: 1857, comm: getty Not tainted (2.6.30 #416)
[  868.082651] EIP: 0060:[<414772ea>] EFLAGS: 00000002 CPU: 0
[  868.095379] EIP is at tty_ldisc_deref+0x1a/0x70
[  868.103757] EAX: 00000216 EBX: 469e2f40 ECX: 414772e8 EDX: 41bf3870
[  868.115752] ESI: 00000216 EDI: 4766483c EBP: 46f37f3c ESP: 41e22450
[  868.131343]  DS: 007b ES: 007b FS: 00d8 GS: 00e0 SS: 0068
[  868.141609] CR0: 8005003b CR2: 47806e04 CR3: 06b6b000 CR4: 00000690
[  868.155263] DR0: 00000000 DR1: 00000000 DR2: 00000000 DR3: 00000000
[  868.167168] DR6: 00004000 DR7: 00000000
[  868.175228]  [<4146f26d>] tty_read+0x8d/0xc0
[  868.184598]  [<410ca219>] vfs_read+0x99/0x180
[  868.196380]  [<410ca3bd>] sys_read+0x3d/0x70
[  868.206936]  [<41003a6f>] sysenter_do_call+0x12/0x3c
[  868.219746]  [<ffffffff>] 0xffffffff

Thats:

drivers/char/tty_ldisc.c:366
drivers/char/tty_io.c:896

I also saw this a couple of times (it's not my printk):

[ 1266.934668] tty_ldisc_deref: no references.
[ 1267.531655] tty_ldisc_deref: no references.
[ 1267.790096] tty_ldisc_deref: no references.


Vegard
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