On Sat, Jun 16, 2012 at 09:32:19AM -0700, Paul E. McKenney wrote:

On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote:

quoted

From: Yong Zhang <redacted>

1) call_function.lock used in smp_call_function_many() is just to protect
   call_function.queue and &data->refs, cpu_online_mask is outside of the
   lock. And it's not necessary to protect cpu_online_mask,
   because data->cpumask is pre-calculate and even if a cpu is brougt up
   when calling arch_send_call_function_ipi_mask(), it's harmless because
   validation test in generic_smp_call_function_interrupt() will take care
   of it.

2) For cpu down issue, stop_machine() will guarantee that no concurrent
   smp_call_fuction() is processing.

However, there is an effort to get rid of stop_machine() from the
CPU-down path...  So something else will be needed.

Yeah. So Thomas changed the commit log like below:
[
    ipi_call_lock/unlock() lock resp. unlock call_function.lock. This lock
    protects only the call_function data structure itself, but it's
    completely unrelated to cpu_online_mask. The mask to which the IPIs
    are sent is calculated before call_function.lock is taken in
    smp_call_function_many(), so the locking around set_cpu_online() is
    pointless and can be removed.
    
    [ tglx: Massaged changelog ]
]

in tip/smp/hotplug.

Thanks,
Yong

							Thanx, Paul

quoted

Signed-off-by: Yong Zhang <redacted>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <redacted>
Cc: linuxppc-dev@lists.ozlabs.org
---
 arch/powerpc/kernel/smp.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c
index e4cb343..e1417c4 100644
--- a/arch/powerpc/kernel/smp.c
+++ b/arch/powerpc/kernel/smp.c

@@ -571,7 +571,6 @@ void __devinit start_secondary(void *unused)
 	if (system_state == SYSTEM_RUNNING)
 		vdso_data->processorCount++;
 #endif
-	ipi_call_lock();
 	notify_cpu_starting(cpu);
 	set_cpu_online(cpu, true);
 	/* Update sibling maps */

@@ -601,7 +600,6 @@ void __devinit start_secondary(void *unused)
 		of_node_put(np);
 	}
 	of_node_put(l2_cache);
-	ipi_call_unlock();

 	local_irq_enable();

-- 
1.7.5.4

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/

-- 
Only stand for myself