netdev - Re: net_sched 00/07: classful multiqueue dummy scheduler

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Date:	Mon, 07 Sep 2009 19:38:11 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Patrick McHardy <kaber@...sh.net>
CC:	David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: net_sched 00/07: classful multiqueue dummy scheduler

Patrick McHardy a écrit :
> Eric Dumazet wrote:
>> Patrick McHardy a écrit :
>>>> Sep  7 16:37:55 erd kernel: [  217.056813] =============================================================================
>>>> Sep  7 16:37:55 erd kernel: [  217.056865] BUG kmalloc-256: Poison overwritten
>>>> Sep  7 16:37:55 erd kernel: [  217.056910] -----------------------------------------------------------------------------
>>>> Sep  7 16:37:55 erd kernel: [  217.056911]
>>>> Sep  7 16:37:55 erd kernel: [  217.056990] INFO: 0xf6e622bc-0xf6e622bd. First byte 0x76 instead of 0x6b
>>>> Sep  7 16:37:55 erd kernel: [  217.057049] INFO: Allocated in qdisc_alloc+0x1b/0x80 age=154593 cpu=2 pid=5165
>>>> Sep  7 16:37:55 erd kernel: [  217.057094] INFO: Freed in qdisc_destroy+0x88/0xa0 age=139186 cpu=4 pid=5173
>>>> Sep  7 16:37:55 erd kernel: [  217.057139] INFO: Slab 0xc16ddc40 objects=26 used=6 fp=0xf6e62260 flags=0x28040c3
>>>> Sep  7 16:37:55 erd kernel: [  217.057184] INFO: Object 0xf6e62260 @offset=608 fp=0xf6e62850
>>>> Sep  7 16:37:55 erd kernel: [  217.057184]
>>> I'm unable to reproduce this. Could you send me the commands you
>>> used that lead to this?
>>>
>> Sorry, this was *before* your last patch.
>>
>> I tried to have more information, because I was not able to get console messages at crash time on this remote dev machine.
>>
>> enabling SLUB checks got some hint of what the problem was (using memory block after its freeing by qdisc_destroy)
> 
> OK, that probably explains it, the spinlock operations were operating
> on already freed memory.
> 
> I'll do some more testing and will send the final patch if no
> other problems show up.

BTW, you may ignore rate estimation requests on the mq root, since its stats
are updated only by user request, when doing a "tc -s -q qdisc" command, while
estimator is fired by a cyclic timer...


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