Date: Sun, 14 Nov 2004 01:09:43 -0800
From: Andrew Morton <akpm@osdl.org>
To: Jamie Lokier <jamie@shareable.org>
Cc: linux-kernel@vger.kernel.org, rusty@rustcorp.com.au, mingo@elte.hu,
       seto.hidetoshi@jp.fujitsu.com, ahu@ds9a.nl
Subject: Re: Futex queue_me/get_user ordering (was: 2.6.10-rc1-mm5 [u])
Message-Id: <20041114010943.3d56985a.akpm@osdl.org>
In-Reply-To: <20041114090023.GA478@mail.shareable.org>
References: <20041113164048.2f31a8dd.akpm@osdl.org>
	<20041114090023.GA478@mail.shareable.org>
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Emergency Services Jamie Lokier <jamie@shareable.org> wrote:
>
> Revert the patch which moves queue_me(); it's buggy.  It is a bug to
>  move queue_me() after get_user().

yup.

>  It fully explains the blocking threads in Apache and Evolution.
> 
>  Even if it worked, the patch wouldn't have saved any time, as it's a
>  rare condition if the caller is using futex properly.

The patch wasn't supposed to optimise anything.  It fixed a bug which was
causing hangs.  See
ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/patches/2.6/2.6.10-rc1/2.6.10-rc1-mm5/broken-out/futex_wait-fix.patch

Or are you saying that userspace is buggy??
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