Messages in this thread | | | Date | Wed, 17 Aug 2022 14:47:52 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 10/14] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read_locked() |
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On Mon, Jul 04, 2022 at 05:05:10PM +0200, Marco Elver wrote:
> +bool percpu_is_read_locked(struct percpu_rw_semaphore *sem) > +{ > + return per_cpu_sum(*sem->read_count) != 0; > +} > +EXPORT_SYMBOL_GPL(percpu_is_read_locked);
I don't think this is correct; read_count can have spurious increments.
If we look at __percpu_down_read_trylock(), it does roughly something like this:
this_cpu_inc(*sem->read_count); smp_mb(); if (!sem->block) return true; this_cpu_dec(*sem->read_count); return false;
So percpu_is_read_locked() needs to ensure the read_count is non-zero *and* that block is not set.
That said; I really dislike the whole _is_locked family with a passion. Let me try and figure out what you need this for.
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