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? Jan > >> kernel/trace/ring_buffer.c | 1 + >> 1 file changed, 1 insertion(+) >> >> diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c >> index f4fbbfc..6a1939e 100644 >> --- a/kernel/trace/ring_buffer.c >> +++ b/kernel/trace/ring_buffer.c >> @@ -1252,6 +1252,7 @@ rb_allocate_cpu_buffer(struct ring_buffer *buffer, int nr_pages, int cpu) >> init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters); >> init_waitqueue_head(&cpu_buffer->irq_work.waiters); >> init_waitqueue_head(&cpu_buffer->irq_work.full_waiters); >> + cpu_buffer->irq_work.work.flags = IRQ_WORK_HARD_IRQ; >> >> bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()), >> GFP_KERNEL, cpu_to_node(cpu)); >> > > Sebastian > -- 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
