forked from Minki/linux
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>
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@ -3780,7 +3780,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
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* the mutex owner just released it and exited.
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*/
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if (probe_kernel_address(&owner->cpu, cpu))
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goto out;
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return 0;
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#else
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cpu = owner->cpu;
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#endif
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@ -3790,14 +3790,14 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
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* the cpu field may no longer be valid.
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*/
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if (cpu >= nr_cpumask_bits)
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goto out;
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return 0;
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/*
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* We need to validate that we can do a
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* get_cpu() and that we have the percpu area.
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*/
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if (!cpu_online(cpu))
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goto out;
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return 0;
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rq = cpu_rq(cpu);
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@ -3816,7 +3816,7 @@ int mutex_spin_on_owner(struct mutex *lock, struct thread_info *owner)
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cpu_relax();
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}
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out:
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return 1;
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}
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#endif
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