From: Ingo Molnar <mingo@elte.hu>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Darren Hart <dvhltc@us.ibm.com>,
linux-kernel@vger.kernel.org,
Thomas Gleixner <tglx@linutronix.de>,
Rusty Russell <rusty@rustcorp.com.au>
Subject: Re: [PATCH 3/6] futex: add double_unlock_hb()
Date: Thu, 12 Mar 2009 11:10:28 +0100 [thread overview]
Message-ID: <20090312101028.GA7157@elte.hu> (raw)
In-Reply-To: <1236852455.5090.105.camel@laptop>
* Peter Zijlstra <peterz@infradead.org> wrote:
> On Thu, 2009-03-12 at 00:55 -0700, Darren Hart wrote:
> > The futex code uses double_lock_hb() which locks the hb->lock's in pointer
> > value order. There is no parallel unlock routine, and the code unlocks them
> > in name order, ignoring pointer value. This opens up a window for an ABBA
> > deadlock. This patch adds double_unlock_hb() to remove the window as well
> > as refactor the duplicated code segments.
>
> While I don't mind the patch per-se, I'm hard pressed to see
> any deadlock potential in the unordered unlock.
>
> All sites (at least those in the patch) always release both
> locks without taking another in between, therefore one would
> think there's no deadlock possible.
yeah.
The patch is still nice (as you mention), it factors out the
unlock sequence. I'll change the commit message accordingy.
Ingo
next prev parent reply other threads:[~2009-03-12 10:11 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-03-12 7:55 [PATCH 0/6] Futex fixes and cleanups Darren Hart
2009-03-12 7:55 ` [PATCH 1/6] Update futex commentary Darren Hart
2009-03-12 10:24 ` [tip:core/futexes] futex: update " Darren Hart
2009-03-12 7:55 ` [PATCH 2/6] Additional (get|put)_futex_key() fixes Darren Hart
2009-03-12 10:16 ` Ingo Molnar
2009-03-12 13:42 ` Thomas Gleixner
2009-03-12 23:22 ` Darren Hart
2009-03-12 10:24 ` [tip:core/futexes] futex: additional " Darren Hart
2009-03-13 0:20 ` Ingo Molnar
2009-03-13 5:46 ` Darren Hart
2009-03-13 0:24 ` [tip:core/urgent] " Darren Hart
2009-03-12 7:55 ` [PATCH 3/6] futex: add double_unlock_hb() Darren Hart
2009-03-12 10:07 ` Peter Zijlstra
2009-03-12 10:10 ` Ingo Molnar [this message]
2009-03-12 10:58 ` Thomas Gleixner
2009-03-12 15:13 ` Darren Hart
2009-03-12 10:24 ` [tip:core/futexes] " Darren Hart
2009-03-12 7:55 ` [PATCH 4/6] futex: Use current->time_slack_ns for rt tasks too Darren Hart
2009-03-12 10:11 ` Peter Zijlstra
2009-03-12 10:24 ` [tip:core/futexes] futex: use " Darren Hart
2009-03-12 13:53 ` Arjan van de Ven
2009-03-12 14:02 ` Peter Zijlstra
2009-03-12 14:25 ` Thomas Gleixner
2009-03-12 14:48 ` Peter Zijlstra
2009-03-12 15:01 ` Arjan van de Ven
2009-03-12 21:33 ` Darren Hart
2009-03-12 21:43 ` Thomas Gleixner
2009-03-12 21:29 ` Darren Hart
2009-03-12 7:56 ` [PATCH 5/6] futex: unlock before returning -EFAULT Darren Hart
2009-03-12 10:13 ` Peter Zijlstra
2009-03-12 10:47 ` Thomas Gleixner
2009-03-12 11:06 ` Peter Zijlstra
2009-03-12 15:15 ` Darren Hart
2009-03-12 22:17 ` Darren Hart
2009-03-12 10:24 ` [tip:core/futexes] " Darren Hart
2009-03-13 0:24 ` [tip:core/urgent] " Darren Hart
2009-03-12 7:56 ` [PATCH 6/6] futex: cleanup fault logic Darren Hart
2009-03-12 10:15 ` Peter Zijlstra
2009-03-12 15:09 ` Darren Hart
2009-03-12 10:25 ` [tip:core/futexes] futex: clean up " Darren Hart
2009-03-12 12:22 ` [PATCH 0/6] Futex fixes and cleanups Ingo Molnar
2009-03-12 15:21 ` Darren Hart
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