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.
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(-)
From: Paul E. McKenney <hidden> Date: 2012-06-16 16:32:57
On Tue, May 29, 2012 at 03:16:04PM +0800, Yong Zhang wrote:
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.
Thanx, Paul
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
From: Paul E. McKenney <hidden> Date: 2012-06-18 17:14:05
On Mon, Jun 18, 2012 at 10:51:59AM +0800, Yong Zhang wrote:
On Sat, Jun 16, 2012 at 09:32:19AM -0700, Paul E. McKenney wrote:
quoted
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.