linux-kernel - Re: [PATCH -tip] Revert x86, mem: Optimize memcpy by avoiding memory false dependece

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Message-ID: <20100708071153.GH4414@elte.hu>
Date:	Thu, 8 Jul 2010 09:11:53 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:	"Ma, Ling" <ling.ma@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH -tip] Revert x86, mem: Optimize memcpy by avoiding memory
 false dependece


* Mathieu Desnoyers <mathieu.desnoyers@...icios.com> wrote:

> * Ma, Ling (ling.ma@...el.com) wrote:
> > Hi Mathieu
> > 
> > I did git revert as bellow
> >     Revert "x86, mem: Optimize memcpy by avoiding memory false dependece"
> > 
> >     This reverts commit 77ff5e49c20bb72a99a12bfb00dbf90b2302f087.
> > And I found the machine will crash with your config file
> > 
> > Could you revert the patch : 77ff5e49c20bb72a99a12bfb00dbf90b2302f087 on your
> > machine, and check it again ?
> 
> Hi Ling,
> 
> I just successfully booted my machine 3 times in a row with a revert of 
> commit a1e5278e40f16a4611264f8da9e557c16cb6f6ed from -tip. This is actually 
> the same as reverting commit 77ff5e49c20bb72a99a12bfb00dbf90b2302f087, as 
> a1e5278e40f16a4611264f8da9e557c16cb6f6ed is simply a merge of that commit 
> (the diffs are exactly the same).
> 
> Without this revert, the machine gets to:

Please check latest -tip (2a74852 or later), the commit should be gone now.

There's clearly some (boundary-condition?) bug in the assembly code of 
77ff5e49c2.

Thanks,

	Ingo
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