Commit 6881e752 authored Jul 31, 2024 by Thomas Gleixner

tick/broadcast: Move per CPU pointer access into the atomic section



The recent fix for making the take over of the broadcast timer more
reliable retrieves a per CPU pointer in preemptible context.

This went unnoticed as compilers hoist the access into the non-preemptible
region where the pointer is actually used. But of course it's valid that
the compiler keeps it at the place where the code puts it which rightfully
triggers:

  BUG: using smp_processor_id() in preemptible [00000000] code:
       caller is hotplug_cpu__broadcast_tick_pull+0x1c/0xc0

Move it to the actual usage site which is in a non-preemptible region.

Fixes: f7d43dd2 ("tick/broadcast: Make takeover of broadcast hrtimer reliable")
Reported-by: David Wang <00107082@163.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Yu Liao <liaoyu15@huawei.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/all/87ttg56ers.ffs@tglx

parent 8400291e

kernel/time/tick-broadcast.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -1141,7 +1141,6 @@ void tick_broadcast_switch_to_oneshot(void)
		#ifdef CONFIG_HOTPLUG_CPU
		void hotplug_cpu__broadcast_tick_pull(int deadcpu)
		{
		struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
		struct clock_event_device *bc;
		unsigned long flags;

		@@ -1167,6 +1166,8 @@ void hotplug_cpu__broadcast_tick_pull(int deadcpu)
		* device to avoid the starvation.
		*/
		if (tick_check_broadcast_expired()) {
		struct tick_device *td = this_cpu_ptr(&tick_cpu_device);

		cpumask_clear_cpu(smp_processor_id(), tick_broadcast_force_mask);
		tick_program_event(td->evtdev->next_event, 1);
		}