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

Sebastian Andrzej Siewior
2024-03-12T18:08:20Z

Hi,

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.

Sebastian