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From: Thomas Gleixner <tglx@linutronix.de>
To: Darren Hart <darren@dvhart.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Ingo Molnar <mingo@kernel.org>,
	Davidlohr Bueso <davidlohr@hp.com>, Kees Cook <kees@outflux.net>,
	wad@chromium.org
Subject: Re: [patch 5/5] futex: Simplify futex_lock_pi_atomic() and make it more robust
Date: Fri, 13 Jun 2014 11:36:54 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.10.1406131136140.5170@nanos> (raw)
In-Reply-To: <alpine.DEB.2.10.1406131033440.5170@nanos>

On Fri, 13 Jun 2014, Thomas Gleixner wrote:
> On Thu, 12 Jun 2014, Darren Hart wrote:
> 
> > On Wed, 2014-06-11 at 20:45 +0000, Thomas Gleixner wrote:
> > > futex_lock_pi_atomic() is a maze of retry hoops and loops.
> > > 
> > > Reduce it to simple and understandable states:
> > 
> > Heh... well...
> > 
> > With this patch applied (1-4 will not reproduce without 5), if userspace
> > wrongly sets the uval to 0, the pi_state can end up being NULL for a
> > subsequent requeue_pi operation:
> > 
> > [   10.426159] requeue: 00000000006022e0 to 00000000006022e4
> > [   10.427737]   this:ffff88013a637da8
> > [   10.428749]   waking:ffff88013a637da8
> > fut2 = 0
> > [   10.429994]   comparing requeue_pi_key
> > [   10.431034]   prepare waiter to take the rt_mutex
> > [   10.432344]   pi_state:          (null)
> > [   10.433414] BUG: unable to handle kernel NULL pointer dereference at
> > 0000000000000038
> > 
> > This occurs in the requeue loop, in the requeue_pi block at:
> > 
> > 	atomic_inc(&pi_state->refcount);
> 
> Hmm. Took me some time to reproduce. Digging into it now.

I'm a moron. Ran out of brown paperbags ....

  reply	other threads:[~2014-06-13  9:37 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-06-11 20:45 [patch 0/5] futex: More robustness tweaks Thomas Gleixner
2014-06-11 20:45 ` [patch 1/5] futex: Make unlock_pi more robust Thomas Gleixner
2014-06-16 16:18   ` Darren Hart
2014-06-16 22:15     ` Thomas Gleixner
2014-06-16 22:28       ` Thomas Gleixner
2014-06-16 22:49         ` Darren Hart
2014-06-16 22:39       ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 3/5] futex: Split out the waiter check from lookup_pi_state() Thomas Gleixner
2014-06-16 18:12   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 2/5] futex: Use futex_top_waiter() in lookup_pi_state() Thomas Gleixner
2014-06-16 16:51   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 4/5] futex: Split out the first waiter attachment from lookup_pi_state() Thomas Gleixner
2014-06-16 18:19   ` Darren Hart
2014-06-21 20:33   ` [tip:locking/core] " tip-bot for Thomas Gleixner
2014-06-11 20:45 ` [patch 5/5] futex: Simplify futex_lock_pi_atomic() and make it more robust Thomas Gleixner
2014-06-13  5:46   ` Darren Hart
2014-06-13  8:34     ` Thomas Gleixner
2014-06-13  9:36       ` Thomas Gleixner [this message]
2014-06-13  9:44         ` [patch V2 " Thomas Gleixner
2014-06-13 20:51           ` Davidlohr Bueso
2014-06-16 20:36           ` Darren Hart
2014-06-17  7:20             ` Thomas Gleixner
2014-06-21 20:34           ` [tip:locking/core] " tip-bot for Thomas Gleixner

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