linux-kernel - [tip: timers/urgent] tick: Remove pointless cpu valid check in hotplug code

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Date:   Wed, 16 Dec 2020 10:50:35 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Frederic Weisbecker <frederic@...nel.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: timers/urgent] tick: Remove pointless cpu valid check in hotplug code

The following commit has been merged into the timers/urgent branch of tip:

Commit-ID:     f12ad423c4af877b2e4b5a80928b95195fccab04
Gitweb:        https://git.kernel.org/tip/f12ad423c4af877b2e4b5a80928b95195fccab04
Author:        Thomas Gleixner <tglx@...utronix.de>
AuthorDate:    Sun, 06 Dec 2020 22:12:54 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 16 Dec 2020 11:26:27 +01:00

tick: Remove pointless cpu valid check in hotplug code

tick_handover_do_timer() which is invoked when a CPU is unplugged has a
check for cpumask_first(cpu_online_mask) when it tries to hand over the
tick update duty.

Checking the result of cpumask_first() there is pointless because if the
online mask is empty at this point, then this would be the last CPU in the
system going offline, which is impossible. There is always at least one CPU
remaining. If online mask would be really empty then the timer duty would
be the least of the resulting problems.

Remove the well meant check simply because it is pointless and confusing.

Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
Link: https://lore.kernel.org/r/20201206212002.582579516@linutronix.de

---
 kernel/time/tick-common.c | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/time/tick-common.c b/kernel/time/tick-common.c
index a03764d..9d3a225 100644
--- a/kernel/time/tick-common.c
+++ b/kernel/time/tick-common.c
@@ -407,17 +407,13 @@ EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
 /*
  * Transfer the do_timer job away from a dying cpu.
  *
- * Called with interrupts disabled. Not locking required. If
+ * Called with interrupts disabled. No locking required. If
  * tick_do_timer_cpu is owned by this cpu, nothing can change it.
  */
 void tick_handover_do_timer(void)
 {
-	if (tick_do_timer_cpu == smp_processor_id()) {
-		int cpu = cpumask_first(cpu_online_mask);
-
-		tick_do_timer_cpu = (cpu < nr_cpu_ids) ? cpu :
-			TICK_DO_TIMER_NONE;
-	}
+	if (tick_do_timer_cpu == smp_processor_id())
+		tick_do_timer_cpu = cpumask_first(cpu_online_mask);
 }
 
 /*