linux-kernel - Re: [PATCH 2/7] sched: Fix picking a task switching on other cpu (__ARCH_WANT_UNLOCKED

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Message-ID: <20140920185434.GE3037@worktop.localdomain>
Date:	Sat, 20 Sep 2014 20:54:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Kirill Tkhai <tkhai@...dex.ru>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Kirill Tkhai <ktkhai@...allels.com>, ralf@...ux-mips.org
Subject: Re: [PATCH 2/7] sched: Fix picking a task switching on other cpu
 (__ARCH_WANT_UNLOCKED_CTXSW)

On Sat, Sep 20, 2014 at 08:33:26PM +0200, Peter Zijlstra wrote:
> On Sat, Sep 20, 2014 at 08:51:22PM +0400, Kirill Tkhai wrote:
> > From: Kirill Tkhai <ktkhai@...allels.com>
> > 
> > We may pick a task which is in context_switch() on other cpu at the moment.
> > Parallel using of a single stack by two processes is not a good idea.
> 
> Please elaborate on who exactly that might happen. Its best to have
> comprehensive changelogs for issues that fix races.

FWIW IIRC we can remove UNLOCKED_CTXSW from IA64 and I forgot if I
audited MIPS, but I suspect we can (and should) remove it there too.

That would make this exception go away and clean up some of this ugly.
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