Re: [PATCH v1] perf test task-exit: Fix POLLHUP busy-loop race waiting for SIGCHLD

[sashiko-bot@kernel.org]

> In the kernel's do_exit(), perf_event_exit_task() runs before exit_mm()
> and exit_notify() (which delivers SIGCHLD to the parent). Once
> perf_event_exit_task() completes, PERF_RECORD_EXIT is written to the
> ring buffer and POLLHUP is set on the perf event file descriptor.
> 
> In test__task_exit(), once POLLHUP is set on the fd, evlist__poll()
> returns immediately on every call without blocking. If the child is
> still in exit_mm()..exit_notify() on another CPU when the parent reads
> PERF_RECORD_EXIT, exited is still 0 and the retry loop spins through all
> 1000 non-blocking poll() calls in less than a millisecond before SIGCHLD
> is delivered.
> 
> Sleep briefly with usleep(1000) on subsequent retries (which also wakes
> early on EINTR when SIGCHLD arrives), mark exited as volatile
> sig_atomic_t, and reset exited and nr_exit on test entry.
> 
> Fixes: 791ce9c48c79 ("perf test: Avoid infinite loop for task exit case")
> Signed-off-by: Ian Rogers <irogers@google.com>

Sashiko has reviewed this patch and found no issues.

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Sashiko AI review · https://sashiko.dev/#/patchset/20261025214928.1225895-1-irogers@google.com?part=1