linux-kernel - Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing the freezing of tasks (rev. 2)

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Message-Id: <1183497552.3388.8.camel@localhost.localdomain>
Date:	Wed, 04 Jul 2007 07:19:12 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Oleg Nesterov <oleg@...sign.ru>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Uli Luckas <u.luckas@...d.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH -mm] PM: Prevent frozen user mode helpers from failing
	the freezing of tasks (rev. 2)


> 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.


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