• Sebastien Dugue's avatar
    hrtimers: allow the hot-unplugging of all cpus · 94df7de0
    Sebastien Dugue authored
    Impact: fix CPU hotplug hang on Power6 testbox
    
    On architectures that support offlining all cpus (at least powerpc/pseries),
    hot-unpluging the tick_do_timer_cpu can result in a system hang.
    
    This comes from the fact that if the cpu going down happens to be the
    cpu doing the tick, then as the tick_do_timer_cpu handover happens after the
    cpu is dead (via the CPU_DEAD notification), we're left without ticks,
    jiffies are frozen and any task relying on timers (msleep, ...) is stuck.
    That's particularly the case for the cpu looping in __cpu_die() waiting
    for the dying cpu to be dead.
    
    This patch addresses this by having the tick_do_timer_cpu handover happen
    earlier during the CPU_DYING notification. For this, a new clockevent
    notification type is introduced (CLOCK_EVT_NOTIFY_CPU_DYING) which is triggered
    in hrtimer_cpu_notify().
    Signed-off-by: default avatarSebastien Dugue <sebastien.dugue@bull.net>
    Cc: <stable@kernel.org>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    94df7de0
hrtimer.c 42.5 KB