From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Vegard Nossum" <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Subject: Re: [Bug #11989] Suspend failure on NForce4-based boards due to chanes in stop_machine
Date: Tue, 11 Nov 2008 14:36:19 +0100
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To: Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org>
Cc: "Rafael J. Wysocki" <rjw-KKrjLPT3xs0@public.gmane.org>, Heiko Carstens <heiko.carstens-tA70FqPdS9bQT0dZR+AlfA@public.gmane.org>, Linux Kernel Mailing List <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Kernel Testers List <kernel-testers-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>, Rusty Russell <rusty-8n+1lVoiYb80n/F98K4Iww@public.gmane.org>, Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>, Oleg Nesterov <oleg-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Dmitry Adamushko <dmitry.adamushko-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>

On Tue, Nov 11, 2008 at 11:52 AM, Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> 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