Message-ID: <4204020F.2000501@yahoo.com.au>
Date: Sat, 05 Feb 2005 10:15:27 +1100
From: Nick Piggin <nickpiggin@yahoo.com.au>
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To: Andrew Morton <akpm@osdl.org>
CC: bstroesser@fujitsu-siemens.com, roland@redhat.com, jdike@addtoit.com,
       blaisorblade_spam@yahoo.it, user-mode-linux-devel@lists.sourceforge.net,
       linux-kernel@vger.kernel.org
Subject: Re: Race condition in ptrace
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Andrew Morton wrote:
> Nick Piggin <nickpiggin@yahoo.com.au> wrote:
> 
>>Bodo Stroesser wrote:
>>
>>>Nick Piggin wrote:
>>>
>>>
>>>>Bodo Stroesser wrote:
>>
>>>>I don't see how this could help because AFAIKS, child->saving is only
>>>>set and cleared while the runqueue is locked. And the same runqueue lock
>>>>is taken by wait_task_inactive.
>>>>
>>>
>>>Sorry, that not right. There are some routines called by sched(), that 
>>>release
>>>and reacquire the runqueue lock.
>>>
>>
>>Oh yeah, it is the wake_sleeping_dependent / dependent_sleeper crap.
>>Sorry, you are right. And that's definitely a bug in sched.c, because
>>it breaks wait_task_inactive, as you've rightly observed.
>>
>>Andrew, IMO this is another bug to hold 2.6.11 for.
> 
> 
> Sure.  I wouldn't consider Bodo's patch to be the one to use though..

No. Something similar could be done that works on all architectures
and all wait_task_inactive callers (and is confined to sched.c). That
would still be more or less a hack to work around smtnice's unfortunate
locking though.

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