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: f7d43dd206e7 ("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

diff --git a/kernel/time/tick-broadcast.c b/kernel/time/tick-broadcast.c
index b4843099a8da74ad79903e8ea9d59b260006f277..ed58eebb4e8f423cf0af169b17b09d94061cbb6a 100644 (file)
--- a/kernel/time/tick-broadcast.c
+++ b/kernel/time/tick-broadcast.c
@@ -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);
                }