linux-kernel - RE: Add memory barrier when waiting on futex

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Message-ID: <3917C05D9F83184EAA45CE249FF1B1DD0253020C@SHSMSX103.ccr.corp.intel.com>
Date:	Wed, 27 Nov 2013 00:28:22 +0000
From:	"Ma, Xindong" <xindong.ma@...el.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	"stable@...r.kernel.org" <stable@...r.kernel.org>,
	"stable-commits@...r.kernel.org" <stable-commits@...r.kernel.org>,
	"Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
	"ccross@...gle.com" <ccross@...gle.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"dvhart@...ux.intel.com" <dvhart@...ux.intel.com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"Tu, Xiaobing" <xiaobing.tu@...el.com>
Subject: RE: Add memory barrier when waiting on futex


> -----Original Message-----
> From: Peter Zijlstra [mailto:peterz@...radead.org]
> Sent: Tuesday, November 26, 2013 4:26 PM
> To: Ma, Xindong
> Cc: stable@...r.kernel.org; stable-commits@...r.kernel.org; Wysocki, Rafael
> J; ccross@...gle.com; tglx@...utronix.de; dvhart@...ux.intel.com;
> mingo@...nel.org; linux-kernel@...r.kernel.org; gregkh@...uxfoundation.org;
> Tu, Xiaobing
> Subject: Re: Add memory barrier when waiting on futex
> 
> On Tue, Nov 26, 2013 at 01:07:25AM +0000, Ma, Xindong wrote:
> > I've already aware that they've protected by spinlock, this is why I adding a
> memory barrier to fix it.
> 
> That doesn't make sense.. the spinlocks should provide the required
> serialization, there's nothing to fix.
> 
> > I reproduced this issue several times on android which running on IA dual
> core.
> 
> I think you need to be more specific, in particular, if spinlocks do not provide
> serialization on your IA32 device, I'd call that thing broken.
> Adding random memory barriers is _WRONG_.
> 
I agree with you. Thanks, Peter.
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