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Subject: Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing
	the freezing of tasks (rev. 2)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>, Pavel Machek <pavel@ucw.cz>,
       Andrew Morton <akpm@linux-foundation.org>,
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Date: Wed, 04 Jul 2007 07:19:12 +1000
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> Actually, spinlock_t is not suitable. Because spin_unlcok() does NOT imply
> mb(). The subsequent wait_event_timeout()->atomic_read() may leak into the
> critical section.
> 
> We can use set_mb(), if we don't want to play with smp_mb() by hand :)

spin_unlock implies a smp_wmb() but yeah, not a full mb(), though having
a read leak into a critical section is generally not an issue.

Ben.