Hi Shaohua,
The patch i submitted only has fix for x86_64. I did not yet submit one
for i386 yet. For x86_64, the whole access for __smp_call_function() is
with call_lock held, so shouldnt be a problem.
Cheers,
ashok
On Tue, Jun 07, 2005 at 03:13:30PM +0800, Shaohua Li wrote:
> On Mon, 2005-06-06 at 12:14 -0700, Ashok Raj wrote:
> > plain text document attachment (no_broadcast_ipi.patch)
> > Broadcast IPI's provide un-expected behaviour for cpu hotplug. CPU's in offline
> > state also end up receiving the IPI. Once the cpus become online
> > they receive these stale IPI's which are bad and introduce unexpected
> > behaviour.
> >
> With the patch. smp_call_function still has race. It accesses
> cpu_online_map twice. First calculate online cpu counter and second,
> send the ipi, so it's not atomic. We should do something like this:
>
Deleted....
>
> --- a/arch/i386/kernel/smp.c 2005-04-26 08:47:08.000000000 +0800
> +++ b/arch/i386/kernel/smp.c 2005-05-31 16:37:10.565141944 +0800
> @@ -527,10 +527,13 @@ int smp_call_function (void (*func) (voi
> {
> struct call_data_struct data;
> int cpus;
> + cpumask_t mask;
>
> /* Holding any lock stops cpus from going down. */
> spin_lock(&call_lock);
> - cpus = num_online_cpus()-1;
> + mask = cpu_online_map;
> + cpu_clear(smp_processor_id(), mask);
> + cpus = cpus_weight(mask);
>
> if (!cpus) {
> spin_unlock(&call_lock);
> @@ -551,7 +554,7 @@ int smp_call_function (void (*func) (voi
> mb();
>
> /* Send a message to all other CPUs and wait for them to respond */
> - send_IPI_allbutself(CALL_FUNCTION_VECTOR);
> + send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
>
> /* Wait for response */
> while (atomic_read(&data.started) != cpus)
> --- a/arch/x86_64/kernel/smp.c 2005-04-12 10:12:16.000000000 +0800
> +++ b/arch/x86_64/kernel/smp.c 2005-05-31 16:38:07.613469280 +0800
> @@ -303,8 +303,11 @@ static void __smp_call_function (void (*
> int nonatomic, int wait)
> {
> struct call_data_struct data;
> - int cpus = num_online_cpus()-1;
> + int cpus;
> + cpumask_t mask = cpu_online_map;
>
> + cpu_clear(smp_processor_id(), mask);
> + cpus = cpus_weight(mask);
> if (!cpus)
> return;
>
> @@ -318,7 +321,7 @@ static void __smp_call_function (void (*
> call_data = &data;
> wmb();
> /* Send a message to all other CPUs and wait for them to respond */
> - send_IPI_allbutself(CALL_FUNCTION_VECTOR);
> + send_IPI_mask(mask, CALL_FUNCTION_VECTOR);
>
> /* Wait for response */
> while (atomic_read(&data.started) != cpus)
>
>
--
Cheers,
Ashok Raj
- Open Source Technology Center
-
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