On 04/16/2015 04:28 PM, Jan Kiszka wrote: > On 2015-04-16 16:26, Sebastian Andrzej Siewior wrote: >> On 04/16/2015 04:06 PM, Jan Kiszka wrote: >>> ftrace may trigger rb_wakeups while holding pi_lock which will also be >>> requested via trace_...->...->ring_buffer_unlock_commit->...-> >>> irq_work_queue->raise_softirq->try_to_wake_up. This quickly causes >>> deadlocks when trying to use ftrace under -rt. >>> >>> Resolve this by marking the ring buffer's irq_work as HARD_IRQ. >>> >>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> >>> --- >>> >>> I'm not yet sure if this doesn't push work into hard-irq context that >>> is better not done there on -rt. >> >> everything should be done in the soft-irq. >> >>> >>> I'm also not sure if there aren't more such cases, given that -rt turns >>> the default irq_work wakeup policy around. But maybe we are lucky. >> >> The only thing that is getting done in the hardirq is the FULL_NO_HZ >> thingy. I would be _very_ glad if we could keep it that way. > > Then - to my current understanding - we need an NMI-safe trigger for > soft-irq work. Is there anything like this existing already? Or can we > still use the IPI-based kick without actually doing the work in hard-irq > context? But if you trigger it via IPI it will still run in hardirq context, right? Can you describe how run into this and try to think about it in a quiet moment. It it just enabling the function tracer and running it? > Jan Sebastian -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
