Re: [PATCH v2 0/4] perf: Make SIGTRAP and __perf_pending_irq() work on RT.

Arnaldo Carvalho de Melo
2024-03-13T15:23:35Z

On Wed, Mar 13, 2024 at 03:35:27PM +0100, Marco Elver wrote:
> On Tue, 12 Mar 2024 at 19:08, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> > Arnaldo reported that "perf test sigtrap" fails on PREEMPT_RT. Sending
> > the signal gets delayed until event_sched_out() which then uses
> > task_work_add() for its delivery. This breaks on PREEMPT_RT because the
> > signal is delivered with disabled preemption.

> > While looking at this, I also stumbled upon __perf_pending_irq() which
> > requires disabled interrupts but this is not the case on PREEMPT_RT.

> > This series aim to address both issues while not introducing a new issue
> > at the same time ;)
> > Any testing is appreciated.

> > v1…v2: https://lore.kernel.org/all/20240308175810.2894694-1-bigeasy@linutronix.de/
> > - Marco pointed me to the testsuite that showed two problems:
> > - Delayed task_work from NMI / missing events.
> > Fixed by triggering dummy irq_work to enforce an interrupt for
> > the exit-to-userland path which checks task_work
> > - Increased ref-count on clean up/ during exec.
> > Mostly addressed by the former change. There is still a window
> > if the NMI occurs during execve(). This is addressed by removing
> > the task_work before free_event().
> > The testsuite (remove_on_exec) fails sometimes if the event/
> > SIGTRAP is sent before the sighandler is installed.

> Tested-by: Marco Elver <elver@google.com>

> It does pass the tests in tools/testing/selftests/perf_events (non-RT
> kernel, lockdep enabled). But I do recall this being a particularly
> sharp corner of perf, so any additional testing and review here is
> useful.

Right, I'm testing with the full 'perf test' suite now.

- Arnaldo