linux-kernel - Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop

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Date:	Tue, 11 Nov 2008 14:36:19 +0100
From:	"Vegard Nossum" <vegard.nossum@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Heiko Carstens" <heiko.carstens@...ibm.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Kernel Testers List" <kernel-testers@...r.kernel.org>,
	"Rusty Russell" <rusty@...tcorp.com.au>,
	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>,
	"Oleg Nesterov" <oleg@...hat.com>,
	"Dmitry Adamushko" <dmitry.adamushko@...il.com>,
	"Andrew Morton" <akpm@...ux-foundation.org>
Subject: Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop_machine

On Tue, Nov 11, 2008 at 11:52 AM, Ingo Molnar <mingo@...e.hu> wrote:
> [ Cc:-ed workqueue/locking/suspend-race-condition experts. ]

Heh. I am not expert, but I looked at the code. The obvious suspicious
thing to see is the use of unpaired barriers? Maybe like this:

 47 static void set_state(enum stopmachine_state newstate)
48 {
49         /* Reset ack counter. */
50         atomic_set(&thread_ack, num_threads);
51         smp_wmb();

+ /* force ordering between thread_ack/state */

52         state = newstate;
53 }
54
55 /* Last one to ack a state moves to the next state. */
56 static void ack_state(void)
57 {
58         if (atomic_dec_and_test(&thread_ack))

Maybe
+ /* force ordering between thread_ack/state */
+ smp_rmb();
here?

59                 set_state(state + 1);
60 }
61

Or maybe I am wrong. But Documentation/memory-barriers.txt is rather
explicit on this point.


Vegard

-- 
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
	-- E. W. Dijkstra, EWD1036
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