Re: [PATCH 1/2] brw_mutex: big read-write mutex

From: Mikulas Patocka
Date: Thu Oct 18 2012 - 15:49:09 EST

On Thu, 18 Oct 2012, Oleg Nesterov wrote:

> Ooooh. And I just noticed include/linux/percpu-rwsem.h which does
> something similar. Certainly it was not in my tree when I started
> this patch... percpu_down_write() doesn't allow multiple writers,
> but the main problem it uses msleep(1). It should not, I think.

synchronize_rcu() can sleep for hundred milliseconds, so msleep(1) is not
a big problem.

> But. It seems that percpu_up_write() is equally wrong? Doesn't
> it need synchronize_rcu() before "p->locked = false" ?

Yes, it does ... and I sent patch for that to Linus.

> (add Mikulas)
> Oleg.

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