linux-kernel - Re: [BUG] futex_unlock_pi() hurts my brain and may cause application deadlock

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Message-Id: <1180574993.21781.22.camel@localhost.localdomain>
Date:	Wed, 30 May 2007 21:29:53 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	john stultz <johnstul@...ibm.com>
Cc:	lkml <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Sripathi Kodi <sripathik@...ibm.com>
Subject: Re: [BUG] futex_unlock_pi() hurts my brain and may cause
	application deadlock

On Wed, 2007-05-30 at 17:49 -0700, john stultz wrote:

> ...
> retry_locked:
> 	/*
> 	 * To avoid races, try to do the TID -> 0 atomic transition
> 	 * again. If it succeeds then we can return without waking
> 	 * anyone else up:
> 	 */
> 	if (!(uval & FUTEX_OWNER_DIED)) {
> 		pagefault_disable();
> 		uval = futex_atomic_cmpxchg_inatomic(uaddr, current->pid, 0);
> 		pagefault_enable();
> 	}

My question is to all the futex gurus out there.

This code is in futex_unlock_pi.  Can the owner of the mutex really die?
Isn't the owner the one doing the unlock?

-- Steve


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