On 2015-04-16 16:57, Sebastian Andrzej Siewior wrote: > 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? # trace-cmd record -e sched /sys/kernel/debug/tracing/events/sched/filter /sys/kernel/debug/tracing/events/*/sched/filter Hit Ctrl^C to stop recording ^C and you are dead(locked). Jan -- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux -- 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
