linux-kernel - Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()" locks up on ARM

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Date:	Sun, 29 May 2011 13:01:58 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Catalin Marinas <catalin.marinas@....com>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Frank Rowand <frank.rowand@...sony.com>,
	Oleg Nesterov <oleg@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Yong Zhang <yong.zhang0@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [BUG] "sched: Remove rq->lock from the first half of ttwu()"
 locks up on ARM

On Sunday, 29 May 2011, Russell King - ARM Linux <linux@....linux.org.uk> wrote:
> On Sun, May 29, 2011 at 11:21:19AM +0100, Catalin Marinas wrote:
>> To avoid extra per-thread flags, we could set a per-cpu variable in
>> switch_mm() so that we know what to switch the page tables to in the
>> post-switch hook.
>
> Why do we need to add more per-cpu stuff when we already have easy access
> to the thread flags?

It could work, I was thinking that we only get an mm structure in the
post-switch hook.

BTW, we currently have a per-cpu current_mm variable in context.c
because switch_mm() is called before switch_to() and the CPU may
receive an IPI to reset the ASID in this interval. But we can remove
it entirely if we set the ASID in the post-switch hook and run the
main switch code with interrupts disabled.


-- 
Catalin
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