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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 <[email protected]> Signed-off-by: Peter Zijlstra <[email protected]> LKML-Reference: <1271212509.13059.135.camel@pasglop> Signed-off-by: Ingo Molnar <[email protected]>
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