From: Greg KH on
2.6.32-stable review patch. If anyone has any objections, please let us know.


From: Benjamin Herrenschmidt <benh(a)>

commit 4b402210486c6414fe5fbfd85934a0a22da56b04 upstream.

Due to recent load-balancer changes that delay the task migration to
the next wakeup, the adaptive mutex spinning ends up in a live lock
when the owner's CPU gets offlined because the cpu_online() check
lives before the owner running check.

This patch changes mutex_spin_on_owner() to return 0 (don't spin) in
any case where we aren't sure about the owner struct validity or CPU
number, and if the said CPU is offline. There is no point going back &
re-evaluate spinning in corner cases like that, let's just go to

Signed-off-by: Benjamin Herrenschmidt <benh(a)>
Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)>
LKML-Reference: <1271212509.13059.135.camel(a)pasglop>
Signed-off-by: Ingo Molnar <mingo(a)>
Signed-off-by: Greg Kroah-Hartman <gregkh(a)>

kernel/sched.c | 8 ++++----
1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -5590,7 +5590,7 @@ int mutex_spin_on_owner(struct mutex *lo
* the mutex owner just released it and exited.
if (probe_kernel_address(&owner->cpu, cpu))
- goto out;
+ return 0;
cpu = owner->cpu;
@@ -5600,14 +5600,14 @@ int mutex_spin_on_owner(struct mutex *lo
* the cpu field may no longer be valid.
if (cpu >= nr_cpumask_bits)
- goto out;
+ return 0;

* We need to validate that we can do a
* get_cpu() and that we have the percpu area.
if (!cpu_online(cpu))
- goto out;
+ return 0;

rq = cpu_rq(cpu);

@@ -5626,7 +5626,7 @@ int mutex_spin_on_owner(struct mutex *lo

return 1;

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