Re: [PATCH] slow_work_execute() needs mb() before test_bit(SLOW_WORK_PENDING)

[Oleg Nesterov <oleg@redhat.com>]

On 04/13, Oleg Nesterov wrote:
>
> slow_work_execute:
>
> 	clear_bit_unlock(SLOW_WORK_EXECUTING, &work->flags);
>
> 	if (test_bit(SLOW_WORK_PENDING, &work->flags) {
>
> clear_bit_unlock() implies release semantics, iow we have a one-way barrier
> before clear_bit(). But we need the mb() semantics after clear_bit(), before
> we test SLOW_WORK_PENDING. Otherwise we can miss SLOW_WORK_ENQ_DEFERRED if
> we race slow_work_enqueue().

However, given that both clear_bit() and set_bit() use the same word, perhaps
this is not possible.

But in that case I don't understand why do we need clear_bit_unlock(), not just
clear_bit(), and how "mb is not needeed" could be derived from documentation.

Oleg.