linux-kernel - Re: [BUG] wireless : cpu stuck for 61s

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Date:	Wed, 6 Aug 2008 09:53:21 +0800
From:	"Dave Young" <hidave.darkstar@...il.com>
To:	"Bob Copeland" <me@...copeland.com>
Cc:	"Jiri Slaby" <jirislaby@...il.com>,
	"Pekka J Enberg" <penberg@...helsinki.fi>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Johannes Berg" <johannes@...solutions.net>,
	linux-kernel@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: [BUG] wireless : cpu stuck for 61s

On Wed, Aug 6, 2008 at 9:51 AM, Dave Young <hidave.darkstar@...il.com> wrote:
> On Tue, Aug 5, 2008 at 8:24 PM, Bob Copeland <me@...copeland.com> wrote:
>> On Tue, Aug 05, 2008 at 09:29:26AM +0800, Dave Young wrote:
>>> With the patch I cann't reproduce the bug with 27-rc1 now.
>>>
>>> >  [<c02375a6>] ? debugfs_create_file+0x46/0x210
>>> >  [<c02375a6>] ? debugfs_create_file+0x46/0x210
>>> >  [<c02375a6>] debugfs_create_file+0x46/0x210
>>> >  [<c02377f1>] debugfs_create_dir+0x21/0x30
>>> >  [<f8901f6d>] ieee80211_sta_debugfs_add+0x2d/0x150 [mac80211]
>>> >  [<f88eba89>] sta_info_debugfs_add_work+0x89/0x130 [mac80211]
>>> >  [<f890a170>] ? rate_control_pid_add_sta_debugfs+0x0/0x30 [mac80211]
>>
>> I wonder if there were two separate problems here.  I looked into
>> this with some detail yesterday and agree with Johannes that the above
>> trace is on locking the parent directory's i_mutex, but I too couldn't
>> see any problems with sta_info_debugfs_add_work.  Other stuff could also
>> modify the directory with or without rtnl_lock, but not in a way that
>> to my untrained eyes would lead to deadlock.
>
> Yes,. I think so. It's the original bug for me, while testing I found
> the mutex deadlock problem.
>
> But this week I will have no time to trace it. so if I have time I
> will keep tracing the problem

Additional info,

With the mutex fix patch, in 2.6.27-rc1 I seems can not reproduce the
debugfs_add bug, (maybe need more test)

But with 2.6.26, the bug can be reproduced. (The mutex fix patch need
not to be applied because there's no such deadlock bug)

>
>>
>> Or is the trace just wrong?
>>
>> --
>> Bob Copeland %% www.bobcopeland.com
>>
>>
>
>
>
> --
> Regards
> dave
>



-- 
Regards
dave
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