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mutex: Don't spin when the owner CPU is offline or other weird cases 

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
sleep.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1271212509.13059.135.camel@pasglop>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
This commit is contained in:
Benjamin Herrenschmidt 2010-04-16 23:20:00 +02:00 committed by Ingo Molnar
parent d5a30458a9
commit 4b40221048
1 changed files with 4 additions and 4 deletions
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8
kernel/sched.c
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@ -3780,7 +3780,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
* the mutex owner just released it and exited.
*/
if (probe_kernel_address(&owner->cpu, cpu))
goto out;
return 0;
#else
cpu = owner->cpu;
#endif
@ -3790,14 +3790,14 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
* 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);
@ -3816,7 +3816,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
cpu_relax();
}
out:
return 1;
}
#endif