Re: [PATCH v3 18/19] perf mutex: Add a robust, process-shared mutex initializer

[sashiko-bot@kernel.org]

> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> A mutex held by a process that can die before unlocking it, like the
> tests forked by 'perf test' that will take turns using the per user
> budget set in kernel.perf_event_mlock_kb, has to be taken over by the
> next locker instead of staying locked forever.
> 
> Robust mutexes, on top of the kernel's robust futexes, do that: when an
> owner dies while holding it the kernel marks the futex word owner-died
> and the next pthread_mutex_lock() returns EOWNERDEAD, then mutex_lock()
> makes it consistent and takes it over; mutex_trylock() and cond_wait()
> come back with EOWNERDEAD too, so they take it over the same way, with
> mutex_trylock() giving the mutex back when it can't be taken over: it
> is held all the same, and a failed trylock must not leak it.
> 
> Add mutex_init_pshared_robust(), returning false when robust mutexes
> aren't available: from libcs without the API, gated by a feature check,
> to musl and glibc refusing them at runtime, when get_robust_list(2) or
> set_robust_list(2) aren't usable.  glibc only sets a flag in
> pthread_mutexattr_setrobust(), refusing the mutex itself in
> pthread_mutex_init() with ENOTSUP instead, other errors from it still
> being reported.  Robust mutexes being unavailable isn't an error, just a
> debug message for whoever then falls back.
> 
> Assisted-by: LLM
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20261016001843.71978-1-acme@kernel.org?part=18