4.19-stable review patch. If anyone has any objections, please let me know.
------------------
From: Frederic Weisbecker frederic@kernel.org
commit dad6a09f3148257ac1773cd90934d721d68ab595 upstream.
The hrtimers migration on CPU-down hotplug process has been moved earlier, before the CPU actually goes to die. This leaves a small window of opportunity to queue an hrtimer in a blind spot, leaving it ignored.
For example a practical case has been reported with RCU waking up a SCHED_FIFO task right before the CPUHP_AP_IDLE_DEAD stage, queuing that way a sched/rt timer to the local offline CPU.
Make sure such situations never go unnoticed and warn when that happens.
Fixes: 5c0930ccaad5 ("hrtimers: Push pending hrtimers away from outgoing CPU earlier") Reported-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Frederic Weisbecker frederic@kernel.org Signed-off-by: Paul E. McKenney paulmck@kernel.org Signed-off-by: Thomas Gleixner tglx@linutronix.de Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20240129235646.3171983-4-boqun.feng@gmail.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- include/linux/hrtimer.h | 4 +++- kernel/time/hrtimer.c | 3 +++ 2 files changed, 6 insertions(+), 1 deletion(-)
--- a/include/linux/hrtimer.h +++ b/include/linux/hrtimer.h @@ -182,6 +182,7 @@ enum hrtimer_base_type { * @hang_detected: The last hrtimer interrupt detected a hang * @softirq_activated: displays, if the softirq is raised - update of softirq * related settings is not required then. + * @online: CPU is online from an hrtimers point of view * @nr_events: Total number of hrtimer interrupt events * @nr_retries: Total number of hrtimer interrupt retries * @nr_hangs: Total number of hrtimer interrupt hangs @@ -206,7 +207,8 @@ struct hrtimer_cpu_base { unsigned int hres_active : 1, in_hrtirq : 1, hang_detected : 1, - softirq_activated : 1; + softirq_activated : 1, + online : 1; #ifdef CONFIG_HIGH_RES_TIMERS unsigned int nr_events; unsigned short nr_retries; --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -970,6 +970,7 @@ static int enqueue_hrtimer(struct hrtime enum hrtimer_mode mode) { debug_activate(timer, mode); + WARN_ON_ONCE(!base->cpu_base->online);
base->cpu_base->active_bases |= 1 << base->index;
@@ -1887,6 +1888,7 @@ int hrtimers_prepare_cpu(unsigned int cp cpu_base->softirq_next_timer = NULL; cpu_base->expires_next = KTIME_MAX; cpu_base->softirq_expires_next = KTIME_MAX; + cpu_base->online = 1; return 0; }
@@ -1953,6 +1955,7 @@ int hrtimers_cpu_dying(unsigned int dyin smp_call_function_single(ncpu, retrigger_next_event, NULL, 0);
raw_spin_unlock(&new_base->lock); + old_base->online = 0; raw_spin_unlock(&old_base->lock);
return 0;