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Message-ID: <20090312101028.GA7157@elte.hu> Date: Thu, 12 Mar 2009 11:10:28 +0100 From: Ingo Molnar <mingo@...e.hu> To: Peter Zijlstra <peterz@...radead.org> Cc: Darren Hart <dvhltc@...ibm.com>, linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>, Rusty Russell <rusty@...tcorp.com.au> Subject: Re: [PATCH 3/6] futex: add double_unlock_hb() * Peter Zijlstra <peterz@...radead.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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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