The way the clockevent devices are finally stopped while a CPU is
offlining is currently chaotic. The layout being by order:
1) tick_sched_timer_dying() stops the tick and the underlying clockevent
but only for oneshot case. The periodic tick and its related
clockevent still runs.
2) tick_broadcast_offline() detaches and stops the per-cpu oneshot
broadcast and append it to the released list.
3) Some individual clockevent drivers stop the clockevents (a second time if
the tick is oneshot)
4) Once the CPU is dead, a control CPU remotely detaches and stops
(a 3rd time if oneshot mode) the CPU clockevent and adds it to the
released list.
5) The released list containing the broadcast device released on step 2)
and the remotely detached clockevent from step 4) are unregistered.
These random events can be factorized if the current clockevent is
detached and stopped by the dying CPU at the generic layer, that is
from the dying CPU:
a) Stop the tick
b) Stop/detach the underlying per-cpu oneshot broadcast clockevent
c) Stop/detach the underlying clockevent
d) Release / unregister the clockevents from b) and c)
e) Release / unregister the remaining clockevents from the dying CPU.
This part could be performed by the dying CPU
This way the drivers and the tick layer don't need to care about
clockevent operations during cpuhotplug down. This also unifies the tick
behaviour on offline CPUs between oneshot and periodic modes, avoiding
offline ticks altogether for sanity.
Adopt the simplification.
[ tglx: Remove the WARN_ON() in clockevents_register_device() as that
is called from an upcoming CPU before the CPU is marked online ]
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20241029125451.54574-3-frederic@kernel.org
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