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authorPreeti U Murthy <preeti@linux.vnet.ibm.com>2015-03-30 14:59:19 +0530
committerIngo Molnar <mingo@kernel.org>2015-04-02 14:25:39 +0200
commit345527b1edce8df719e0884500c76832a18211c3 (patch)
tree386a6b25b2437bd94cf63df6d02d95f729eab7cc /kernel/cpu.c
parent9eed56e889d8a0bb7870e1216d8d4326dd63ec50 (diff)
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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/cpu.c')
-rw-r--r--kernel/cpu.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/cpu.c b/kernel/cpu.c
index 1972b161c61e..af5db20e5803 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -20,6 +20,7 @@
#include <linux/gfp.h>
#include <linux/suspend.h>
#include <linux/lockdep.h>
+#include <linux/tick.h>
#include <trace/events/power.h>
#include "smpboot.h"
@@ -411,6 +412,7 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen)
while (!idle_cpu(cpu))
cpu_relax();
+ hotplug_cpu__broadcast_tick_pull(cpu);
/* This actually kills the CPU. */
__cpu_die(cpu);