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Hang is observed on virtual machines during CPU hotplug, especially in big guests with many CPUs. (It reproducible more often if host is over-committed). It happens because master CPU gives up waiting on secondary CPU and allows it to run wild. As result AP causes locking or crashing system. For example as described here: https://lkml.org/lkml/2014/3/6/257 If master CPU have sent STARTUP IPI successfully, and AP signalled to master CPU that it's ready to start initialization, make master CPU wait indefinitely till AP is onlined. To ensure that AP won't ever run wild, make it wait at early startup till master CPU confirms its intention to wait for AP. If AP doesn't respond in 10 seconds, the master CPU will timeout and cancel AP onlining. Signed-off-by: Igor Mammedov <imammedo@redhat.com> Acked-by: Toshi Kani <toshi.kani@hp.com> Cc: Thomas Gleixner <tglx@linutronix.de> Link: http://lkml.kernel.org/r/1401975765-22328-4-git-send-email-imammedo@redhat.com Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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