Messages in this thread | | | Subject | Re: [PATCH] sched_rt: the task in irq context can be migrated during context switching | From | Peter Zijlstra <> | Date | Thu, 05 Jan 2012 22:45:04 +0100 |
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On Thu, 2012-01-05 at 13:15 -0500, Steven Rostedt wrote: > 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.
Its not running, but its in the middle of getting scheduled out.
> 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.
Right, so the post_schedule() hook will try again.
> 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.
Yeah, I'm not sure all those task_running() things make sense though, when !->on_rq && ->on_cpu we should busy wait for tasks, not skip them.
Then again, with this WANT_INTERRUPTS_ON_CTXSW the busy wait crap is tricky. Luckily its going the way of the Dodo very soon.
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