From: Esben Nielsen <simlo@phys.au.dk>
To: Dinakar Guniguntala <dino@in.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>,
robustmutexes@lists.osdl.org, linux-kernel@vger.kernel.org
Subject: Re: Recursion bug in -rt
Date: Tue, 20 Dec 2005 18:43:03 +0100 (MET) [thread overview]
Message-ID: <Pine.OSF.4.05.10512201834580.1720-100000@da410.phys.au.dk> (raw)
In-Reply-To: <20051220155004.GA3906@in.ibm.com>
On Tue, 20 Dec 2005, Dinakar Guniguntala wrote:
> On Tue, Dec 20, 2005 at 02:19:56PM +0100, Ingo Molnar wrote:
> >
> > hm, i'm looking at -rf4 - these changes look fishy:
> >
> > - _raw_spin_lock(&lock_owner(lock)->task->pi_lock);
> > + if (current != lock_owner(lock)->task)
> > + _raw_spin_lock(&lock_owner(lock)->task->pi_lock);
> >
> > why is this done?
> >
>
> Ingo, this is to prevent a kernel hang due to application error.
>
> Basically when an application does a pthread_mutex_lock twice on a
> _nonrecursive_ mutex with robust/PI attributes the whole system hangs.
> Ofcourse the application clearly should not be doing anything like
> that, but it should not end up hanging the system either
>
Hmm, reading the comment on the function, wouldn't it be more natural to
use
if(task != lock_owner(lock)->task)
as it assumes that task->pi_lock is locked, not that current->pi_lock is
locked.
By the way:
task->pi_lock is taken. lock_owner(lock)->task->pi_lock will be taken.
What if the task lock_owner(lock)->task tries to lock another futex,
(lock2) with which has lock_owner(lock2)->task==task.
Can't you promote a user space futex deadlock into a kernel spin deadlock
this way?
Esben
> -Dinakar
>
>
next prev parent reply other threads:[~2005-12-20 17:44 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2005-12-14 22:39 Recursion bug in -rt Dinakar Guniguntala
2005-12-15 1:03 ` david singleton
2005-12-15 19:44 ` Dinakar Guniguntala
2005-12-15 20:40 ` David Singleton
2005-12-16 0:02 ` david singleton
2005-12-16 18:42 ` Dinakar Guniguntala
2005-12-16 21:26 ` David Singleton
2005-12-19 11:56 ` Dinakar Guniguntala
2005-12-19 20:11 ` David Singleton
2005-12-15 19:00 ` David Singleton
2005-12-15 19:52 ` Dinakar Guniguntala
2005-12-20 13:19 ` Ingo Molnar
2005-12-20 15:50 ` Dinakar Guniguntala
2005-12-20 17:43 ` Esben Nielsen [this message]
2005-12-20 19:33 ` Steven Rostedt
2005-12-20 20:42 ` Esben Nielsen
2005-12-20 21:20 ` Steven Rostedt
2005-12-20 21:55 ` david singleton
2005-12-20 22:56 ` Esben Nielsen
2005-12-20 23:12 ` Steven Rostedt
2005-12-20 23:55 ` Esben Nielsen
2005-12-22 4:37 ` david singleton
2005-12-20 22:43 ` Esben Nielsen
2005-12-20 22:59 ` Steven Rostedt
2006-01-03 1:54 ` david singleton
2006-01-05 2:14 ` david singleton
2006-01-05 9:43 ` Esben Nielsen
2006-01-05 17:11 ` david singleton
2006-01-05 17:47 ` Esben Nielsen
2006-01-05 18:26 ` david singleton
2006-01-07 2:40 ` robust futex deadlock detection patch david singleton
[not found] ` <a36005b50601071145y7e2ead9an4a4ca7896f35a85e@mail.gmail.com>
2006-01-07 19:49 ` Ulrich Drepper
2006-01-09 9:23 ` Esben Nielsen
2006-01-09 20:01 ` David Singleton
2006-01-09 20:16 ` Esben Nielsen
2006-01-09 21:08 ` Steven Rostedt
2006-01-09 21:19 ` Esben Nielsen
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