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Message-ID: <51709FE1.20807@codeaurora.org>
Date: Thu, 18 Apr 2013 18:37:37 -0700
From: Michael Bohan <mbohan@codeaurora.org>
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To: Thomas Gleixner <tglx@linutronix.de>
CC: LKML <linux-kernel@vger.kernel.org>, linux-arm-msm@vger.kernel.org,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/2] hrtimer: Consider preemption when migrating hrtimer
 cpu_bases
References: <1365628068-32738-1-git-send-email-mbohan@codeaurora.org> <1365628068-32738-2-git-send-email-mbohan@codeaurora.org> <alpine.LFD.2.02.1304181138290.21884@ionos>
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On 4/18/2013 2:40 AM, Thomas Gleixner wrote:
> On Wed, 10 Apr 2013, Michael Bohan wrote:
>
>> When switching to a new cpu_base in switch_hrtimer_base(), we
>> briefly enable preemption by unlocking the cpu_base lock in two
>> places. During this interval it's possible for the running thread
>> to be swapped to a different CPU.
>>
>> Consider the following example:
>>
>> CPU #0                                 CPU #1
>> ----                                   ----
>> hrtimer_start()                        ...
>>   lock_hrtimer_base()
>>   switch_hrtimer_base()
>>    this_cpu = 0;
>>    target_cpu_base = 0;
>>    raw_spin_unlock(&cpu_base->lock)
>> <migrate to CPU 1>
>
> Errm. switch_hrtimer_base() is called with interrupts disabled and
> they stay disabled, so how exactly is the task going to be migrated?

My mistake - I missed that important fact. Please disregard this.

Thanks,
Mike

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