linux-kernel - Re: [PATCH RT 0/3] Linux 3.10.47-rt50-rc1

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Date:	Wed, 16 Jul 2014 09:31:17 -0500
From:	Corey Minyard <cminyard@...sta.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	linux-kernel@...r.kernel.org,
	linux-rt-users <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Carsten Emde <C.Emde@...dl.org>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	John Kacur <jkacur@...hat.com>,
	Paul Gortmaker <paul.gortmaker@...driver.com>
Subject: Re: [PATCH RT 0/3] Linux 3.10.47-rt50-rc1

On 07/14/2014 07:53 PM, Steven Rostedt wrote:
> On Mon, 14 Jul 2014 19:09:48 -0500
> Corey Minyard <cminyard@...sta.com> wrote:
>
>> Can we get:
>>
>> tracing-use-migrate_disable-to-prevent-beeing-pushed.patch
> Sure except that patch is buggy:
>
> -               preempt_disable();
> +               migrate_disable();
>                 /* The update must run on the CPU that is being updated. */
>                 if (cpu_id == smp_processor_id() || !cpu_online(cpu_id))
>                         rb_update_pages(cpu_buffer);
>                 else {
> -                       /*
> -                        * Can not disable preemption for schedule_work_on()
> -                        * on PREEMPT_RT.
> -                        */
> -                       preempt_enable();
>                         schedule_work_on(cpu_id,
>                                          &cpu_buffer->update_pages_work);
>                         wait_for_completion(&cpu_buffer->update_done);
> -                       preempt_disable();
>                 }
> -               preempt_enable();
> +               migrate_enable();
>
> migrate_disable() on non-PREEMPT_RT is preempt_disable(). You can't
> call wait_or_completion with preemption disabled.
>
> When that gets fixed in mainline -rt, I'll add it to the stable
> branches too.

I originally did a patch that just always did the else clause (the
schedule_work_on() and wait_for_completion()) on all CPUs.  That seemed
to work just fine and simplifies the code a bit and gets rid of all the
preempt/migrate calls.  You could try that approach, or I could submit
something if you liked.

-corey

>
> -- Steve
>
>
>
>> into 3.10, also?
>>

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