On Tue, 2008-11-11 at 14:36 +0100, Vegard Nossum wrote:
quoted text
> On Tue, Nov 11, 2008 at 11:52 AM, Ingo Molnar <mingo@elte.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?

all atomic ops that have return values imply a full barrier, iirc

quoted text
> 59                 set_state(state + 1);
> 60 }
> 61
> 
> Or maybe I am wrong. But Documentation/memory-barriers.txt is rather
> explicit on this point.
> 
> 
> Vegard
> 

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