Re: [PATCH v9 4/9] perf mutex: Add DO_ONCE() for one-time initialization

[sashiko-bot@kernel.org]

> From: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> For lazy init that more than one thread can race into, without
> pthread_once() so that it stays within perf's locking primitives and
> clang's -Wthread-safety keeps an eye on the mutexes involved.
> 
> Mirrors the kernel's include/linux/once.h DO_ONCE(), dropping its
> static key fast path, unnecessary at these cold init paths: a per call
> site static bool plus a statically initialized mutex, double checked.
> As there, code reachable from more than one call site must go through
> a common helper.
> 
> The lockless fast path reads ___done with an acquire, paired with a
> release store after fn(), so that fn()'s side effects are visible to
> threads taking the fast path, which the dropped static key used to
> guarantee.
> 
> The __atomic builtins are used rather than smp_load_acquire()/
> smp_store_release() because ThreadSanitizer understands them,
> avoiding reports on ___done and on what fn() initialized.
> 
> 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/20261004060457.3353-1-acme@kernel.org?part=4