Hang is observed on virtual machines during CPU hotplug, especially in big guests with many CPUs. (It happens more often if host is over-committed). Hang happens because master CPU timeouts on waiting till AP boots and 'cancels' CPU online operation assuming AP is not functional but AP may continue run wild later causing various hangs or panics in running kernel that is assuming that AP was offline. This is an alternative approach, that instead of canceling in-progress AP bringup (https://lkml.org/lkml/2014/3/6/257), removes timeouts so that AP bringup won't be affected by poor timing and syncs AP with master CPU at early startup making sure that AP won't run wild if master CPU doesn't expect AP to come online. Series also fixes 3 bugs found during testing CPU bringup failure case. -- Below is the detailed description of a more often happening hang: --- Master CPU may timeout before cpu_callin_mask is set and cancel booting CPU, but being onlined CPU still continues to boot, sets cpu_active_mask (CPU_STARTING notifiers) and spins in check_tsc_sync_target() for master cpu to arrive. Following attempt to online another cpu hangs in stop_machine, initiated from here: smp_callin -> smp_store_cpu_info -> identify_secondary_cpu -> mtrr_ap_init -> set_mtrr_from_inactive_cpu stop_machine waits on completion of stop_work on all CPUs from cpu_active_mask including a failed CPU that spins in check_tsc_sync_target(). Igor Mammedov (5): x86: initialize secondary CPU only if master CPU will wait for it x86: log error on secondary CPU wakeup failure at ERR level x86: fix list corruption on CPU hotplug x86: fix memory corruption in acpi_unmap_lsapic() acpi_processor: do not mark present at boot but not onlined CPU as onlined arch/x86/kernel/cpu/common.c | 28 +++++++---- arch/x86/kernel/smpboot.c | 103 ++++++++++++---------------------------- drivers/acpi/acpi_processor.c | 3 - 3 files changed, 48 insertions(+), 86 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
