hulk inclusion category: bugfix bugzilla: https://gitee.com/openeuler/kernel/issues/I8PL17 CVE: NA

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It was found that running the LTP hotplug stress test on a aarch64 system could produce rcu_sched stall warnings. The issue is the following:

CPU1 (owns the broadcast hrtimer) CPU2

tick_broadcast_enter() //shut down local timer device ... tick_broadcast_exit() //exits with tick_broadcast_force_mask set, timer device remains disabled

initiates offlining of CPU1 take_cpu_down() //CPU1 shuts down and does not send broadcast IPI anymore takedown_cpu() hotplug_cpu__broadcast_tick_pull() //move broadcast hrtimer to this CPU clockevents_program_event() bc_set_next() hrtimer_start() //does not call hrtimer_reprogram() to program timer device if expires equals dev->next_event, so the timer device remains disabled.

CPU2 takes over the broadcast duty but local timer device is disabled, causing many CPUs to become stuck.

Fix this by calling tick_program_event() to reprogram the local timer device in this scenario.

Signed-off-by: Yu Liao liaoyu15@huawei.com --- kernel/time/tick-broadcast-hrtimer.c | 14 ++++++++++++++ 1 file changed, 14 insertions(+)

diff --git a/kernel/time/tick-broadcast-hrtimer.c b/kernel/time/tick-broadcast-hrtimer.c index b5a65e212df2..b8e79f8012f3 100644 --- a/kernel/time/tick-broadcast-hrtimer.c +++ b/kernel/time/tick-broadcast-hrtimer.c @@ -42,6 +42,8 @@ static int bc_shutdown(struct clock_event_device *evt) */ static int bc_set_next(ktime_t expires, struct clock_event_device *bc) { + struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev); + /* * This is called either from enter/exit idle code or from the * broadcast handler. In all cases tick_broadcast_lock is held. @@ -62,6 +64,18 @@ static int bc_set_next(ktime_t expires, struct clock_event_device *bc) * hrtimer_start() can call into tracing. */ RCU_NONIDLE( { + + /* + * This can be called from CPU offline operation to move broadcast + * assignment. If tick_broadcast_force_mask is set, the CPU local + * timer device may be disabled. And hrtimer_reprogram() will not + * called if the timer is not the first expiring timer. Reprogram + * the cpu local timer device to ensure we can take over the + * broadcast duty. + */ + if (tick_check_broadcast_expired() && expires >= dev->next_event) + clockevents_program_event(dev, dev->next_event, 1); + hrtimer_start(&bctimer, expires, HRTIMER_MODE_ABS_PINNED_HARD); /* * The core tick broadcast mode expects bc->bound_on to be set