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author | Preeti U Murthy <preeti@linux.vnet.ibm.com> | 2015-03-30 09:29:19 (GMT) |
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committer | Ingo Molnar <mingo@kernel.org> | 2015-04-02 12:25:39 (GMT) |
commit | 345527b1edce8df719e0884500c76832a18211c3 (patch) | |
tree | 386a6b25b2437bd94cf63df6d02d95f729eab7cc /include | |
parent | 9eed56e889d8a0bb7870e1216d8d4326dd63ec50 (diff) | |
download | linux-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 'include')
-rw-r--r-- | include/linux/tick.h | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/include/linux/tick.h b/include/linux/tick.h index 589868b..f9ff225 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -36,6 +36,12 @@ extern void tick_irq_enter(void); static inline void tick_irq_enter(void) { } #endif +#if defined(CONFIG_GENERIC_CLOCKEVENTS_BROADCAST) && defined(CONFIG_TICK_ONESHOT) +extern void hotplug_cpu__broadcast_tick_pull(int dead_cpu); +#else +static inline void hotplug_cpu__broadcast_tick_pull(int dead_cpu) { } +#endif + #ifdef CONFIG_NO_HZ_COMMON extern int tick_nohz_tick_stopped(void); extern void tick_nohz_idle_enter(void); |