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author | Max Krasnyansky <maxk@qualcomm.com> | 2008-07-15 20:56:26 -0700 |
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committer | Ingo Molnar <mingo@elte.hu> | 2008-07-18 13:23:18 +0200 |
commit | 39b0fad7121eace85770e7a4c6dc35dfd2879768 (patch) | |
tree | a5d85b06fd656ccb26c906c237fb45dccd46e18c /kernel | |
parent | e761b7725234276a802322549cee5255305a0930 (diff) | |
download | linux-39b0fad7121eace85770e7a4c6dc35dfd2879768.tar.gz linux-39b0fad7121eace85770e7a4c6dc35dfd2879768.tar.bz2 linux-39b0fad7121eace85770e7a4c6dc35dfd2879768.zip |
cpu hotplug: Make cpu_active_map synchronization dependency clear
This goes on top of the cpu_active_map (take 2) patch.
Currently we depend on the stop_machine to provide nescessesary
synchronization for the cpu_active_map updates.
As Dmitry Adamushko pointed this is fragile and is not much clearer
than the previous scheme. In other words we do not want to depend on
the internal stop machine operation here.
So make the synchronization rules clear by doing synchronize_sched()
after clearing out cpu active bit.
Tested on quad-Core2 with:
while true; do
for i in 1 2 3; do
echo 0 > /sys/devices/system/cpu/cpu$i/online
done
for i in 1 2 3; do
echo 1 > /sys/devices/system/cpu/cpu$i/online
done
done
and
stress -c 200
No lockdep, preempt or other complaints.
Signed-off-by: Max Krasnyansky <maxk@qualcomm.com>
Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/cpu.c | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c index a1ac7ea245d7..033603c1d7c3 100644 --- a/kernel/cpu.c +++ b/kernel/cpu.c @@ -301,6 +301,16 @@ int __ref cpu_down(unsigned int cpu) cpu_clear(cpu, cpu_active_map); + /* + * Make sure the all cpus did the reschedule and are not + * using stale version of the cpu_active_map. + * This is not strictly necessary becuase stop_machine() + * that we run down the line already provides the required + * synchronization. But it's really a side effect and we do not + * want to depend on the innards of the stop_machine here. + */ + synchronize_sched(); + err = _cpu_down(cpu, 0); if (cpu_online(cpu)) |