linux-kernel - Re: [PATCH -rt] sched: teach migrate

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Date:	Tue, 6 Sep 2011 15:08:19 -0300
From:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -rt] sched: teach migrate_disable about atomic contexts

Em Fri, Sep 02, 2011 at 02:41:37PM +0200, Peter Zijlstra escreveu:
> Subject: sched: teach migrate_disable about atomic contexts
> From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Date: Fri Sep 02 14:29:27 CEST 2011
> 
>  <NMI>  [<ffffffff812dafd8>] spin_bug+0x94/0xa8
>  [<ffffffff812db07f>] do_raw_spin_lock+0x43/0xea
>  [<ffffffff814fa9be>] _raw_spin_lock_irqsave+0x6b/0x85
>  [<ffffffff8106ff9e>] ? migrate_disable+0x75/0x12d
>  [<ffffffff81078aaf>] ? pin_current_cpu+0x36/0xb0
>  [<ffffffff8106ff9e>] migrate_disable+0x75/0x12d
>  [<ffffffff81115b9d>] pagefault_disable+0xe/0x1f
>  [<ffffffff81047027>] copy_from_user_nmi+0x74/0xe6
>  [<ffffffff810489d7>] perf_callchain_user+0xf3/0x135
> 
> Now clearly we can't go around taking locks from NMI context, cure
> this by short-circuiting migrate_disable() when we're in an atomic
> context already.
> 
> Add some extra debugging to avoid things like:
> 
>   preempt_disable()
>   migrate_disable();
> 
>   preempt_enable();
>   migrate_enable();
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> Link: http://lkml.kernel.org/n/tip-wbot4vsmwhi8vmbf83hsclk6@git.kernel.org

Now I can collect callchains with perf on linux RT, thanks.

Tested-by: Arnaldo Carvalho de Melo <acme@...hat.com>

- Arnaldo
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