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SubjectRe: [PATCH] sched_rt: the task in irq context can be migrated during context switching
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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@goodmis.org>

-- Steve




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