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

Vegard Nossum
2008-11-11T13:36:19Z

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