linux-kernel - Re: [PATCH] sched_rt: the task in irq context can be migrated during context switching

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Message-ID: <1325787342.12696.59.camel@gandalf.stny.rr.com>
Date:	Thu, 05 Jan 2012 13:15:42 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Chanho Min <chanho0207@...il.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>, chanho.min@....com
Subject: Re: [PATCH] sched_rt: the task in irq context can be migrated
 during context switching

On Thu, 2012-01-05 at 18:55 +0100, Peter Zijlstra wrote:

> So the problem is quite real, as already said we don't need to worry
> about the future, but we might want to fix this in previous kernels.
> What I'm not entirely sure of is the proposed solution, Steven don't we
> get in trouble by simply bailing out on the push?

It shouldn't break anything. We shouldn't be pushing tasks that are
running on a rq anyway. I don't see any harm here. As this scenario can
only happen if we get an interrupt after letting go of the rq lock and
before doing the switch_to(). The schedule_tail() calls
post_schedule_rt() which does the push again, and will push task A at
that time.

That said, I'm not sure this patch is enough. I'm worried about a pull
happening. As task A is running, we could possible possibly pick it on
another CPU to do a pull.

Hmm, looking at the code, the pull already does a task_running() test,
so I guess we should be fine.

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

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