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generic-ipi: fix the smp_mb() placement 

smp_mb() is needed (to make the memory operations visible globally) before
sending the ipi on the sender and the receiver (on Alpha atleast) needs
smp_read_barrier_depends() in the handler before reading the call_single_queue
list in a lock-free fashion.

On x86, x2apic mode register accesses for sending IPI's don't have serializing
semantics. So the need for smp_mb() before sending the IPI becomes more
critical in x2apic mode.

Remove the unnecessary smp_mb() in csd_flag_wait(), as the presence of that
smp_mb() doesn't mean anything on the sender, when the ipi receiver is not
doing any thing special (like memory fence) after clearing the CSD_FLAG_WAIT.

Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
This commit is contained in:
Suresh Siddha 2008-10-30 18:28:41 +01:00 committed by Jens Axboe
parent e78042e5b8
commit 561920a0d2
1 changed files with 12 additions and 6 deletions
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18
kernel/smp.c
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@ -51,10 +51,6 @@ static void csd_flag_wait(struct call_single_data *data)
{
/* Wait for response */
do {
/*
* We need to see the flags store in the IPI handler
*/
smp_mb();
if (!(data->flags & CSD_FLAG_WAIT))
break;
cpu_relax();
@ -76,6 +72,11 @@ static void generic_exec_single(int cpu, struct call_single_data *data)
list_add_tail(&data->list, &dst->list);
spin_unlock_irqrestore(&dst->lock, flags);
/*
* Make the list addition visible before sending the ipi.
*/
smp_mb();
if (ipi)
arch_send_call_function_single_ipi(cpu);
@ -157,7 +158,7 @@ void generic_smp_call_function_single_interrupt(void)
* Need to see other stores to list head for checking whether
* list is empty without holding q->lock
*/
smp_mb();
smp_read_barrier_depends();
while (!list_empty(&q->list)) {
unsigned int data_flags;
@ -191,7 +192,7 @@ void generic_smp_call_function_single_interrupt(void)
/*
* See comment on outer loop
*/
smp_mb();
smp_read_barrier_depends();
}
}
@ -370,6 +371,11 @@ int smp_call_function_mask(cpumask_t mask, void (*func)(void *), void *info,
list_add_tail_rcu(&data->csd.list, &call_function_queue);
spin_unlock_irqrestore(&call_function_lock, flags);
/*
* Make the list addition visible before sending the ipi.
*/
smp_mb();
/* Send a message to all CPUs in the map */
arch_send_call_function_ipi(mask);