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authorPreeti U Murthy <preeti@linux.vnet.ibm.com>2015-03-30 12:29:19 +0300
committerIngo Molnar <mingo@kernel.org>2015-04-02 15:25:39 +0300
commit345527b1edce8df719e0884500c76832a18211c3 (patch)
tree386a6b25b2437bd94cf63df6d02d95f729eab7cc /kernel/time/tick-broadcast.c
parent9eed56e889d8a0bb7870e1216d8d4326dd63ec50 (diff)
downloadlinux-345527b1edce8df719e0884500c76832a18211c3.tar.xz
clockevents: Fix cpu_down() race for hrtimer based broadcasting
It was found when doing a hotplug stress test on POWER, that the machine either hit softlockups or rcu_sched stall warnings. The issue was traced to commit: 7cba160ad789 ("powernv/cpuidle: Redesign idle states management") which exposed the cpu_down() race with hrtimer based broadcast mode: 5d1638acb9f6 ("tick: Introduce hrtimer based broadcast") The race is the following: Assume CPU1 is the CPU which holds the hrtimer broadcasting duty before it is taken down. CPU0 CPU1 cpu_down() take_cpu_down() disable_interrupts() cpu_die() while (CPU1 != CPU_DEAD) { msleep(100); switch_to_idle(); stop_cpu_timer(); schedule_broadcast(); } tick_cleanup_cpu_dead() take_over_broadcast() So after CPU1 disabled interrupts it cannot handle the broadcast hrtimer anymore, so CPU0 will be stuck forever. Fix this by explicitly taking over broadcast duty before cpu_die(). This is a temporary workaround. What we really want is a callback in the clockevent device which allows us to do that from the dying CPU by pushing the hrtimer onto a different cpu. That might involve an IPI and is definitely more complex than this immediate fix. Changelog was picked up from: https://lkml.org/lkml/2015/2/16/213 Suggested-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Nicolas Pitre <nico@linaro.org> Signed-off-by: Preeti U. Murthy <preeti@linux.vnet.ibm.com> Cc: linuxppc-dev@lists.ozlabs.org Cc: mpe@ellerman.id.au Cc: nicolas.pitre@linaro.org Cc: peterz@infradead.org Cc: rjw@rjwysocki.net Fixes: http://linuxppc.10917.n7.nabble.com/offlining-cpus-breakage-td88619.html Link: http://lkml.kernel.org/r/20150330092410.24979.59887.stgit@preeti.in.ibm.com [ Merged it to the latest timer tree, renamed the callback, tidied up the changelog. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/time/tick-broadcast.c')
-rw-r--r--kernel/time/tick-broadcast.c19
1 files changed, 11 insertions, 8 deletions
diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index 19cfb381faa9..f5e0fd5652dc 100644
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -680,14 +680,19 @@ static void broadcast_shutdown_local(struct clock_event_device *bc,
clockevents_set_state(dev, CLOCK_EVT_STATE_SHUTDOWN);
}
-static void broadcast_move_bc(int deadcpu)
+void hotplug_cpu__broadcast_tick_pull(int deadcpu)
{
- struct clock_event_device *bc = tick_broadcast_device.evtdev;
+ struct clock_event_device *bc;
+ unsigned long flags;
- if (!bc || !broadcast_needs_cpu(bc, deadcpu))
- return;
- /* This moves the broadcast assignment to this cpu */
- clockevents_program_event(bc, bc->next_event, 1);
+ raw_spin_lock_irqsave(&tick_broadcast_lock, flags);
+ bc = tick_broadcast_device.evtdev;
+
+ if (bc && broadcast_needs_cpu(bc, deadcpu)) {
+ /* This moves the broadcast assignment to this CPU: */
+ clockevents_program_event(bc, bc->next_event, 1);
+ }
+ raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}
/*
@@ -924,8 +929,6 @@ void tick_shutdown_broadcast_oneshot(unsigned int *cpup)
cpumask_clear_cpu(cpu, tick_broadcast_pending_mask);
cpumask_clear_cpu(cpu, tick_broadcast_force_mask);
- broadcast_move_bc(cpu);
-
raw_spin_unlock_irqrestore(&tick_broadcast_lock, flags);
}