linux-kernel - [PATCH v2] hrtimer: Add a missing bracket and hide `migration

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Date:   Wed, 4 Sep 2019 16:55:27 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Julien Grall <julien.grall@....com>
Subject: [PATCH v2] hrtimer: Add a missing bracket and hide `migration_base'
 on !SMP

The recent change to avoid taking the expiry lock when a timer is
currently migrated missed to add a bracket at the end of the if
statement leading to compile errors.
Since that commit the variable `migration_base' is always used but only
available on SMP configuration thus leading to another compile error.
The changelog says
  "The timer base and base->cpu_base cannot be NULL in the code path"

so it is safe to limit this check to SMP configurations only.

Add the missing bracket to the if statement and hide `migration_base'
behind CONFIG_SMP bars.

Fixes: 68b2c8c1e4210 ("hrtimer: Don't take expiry_lock when timer is currently migrated")
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
v1…v2:
	- use is_migration_base() as a helper function
	- slightly reword the commit message

 kernel/time/hrtimer.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/time/hrtimer.c b/kernel/time/hrtimer.c
index f5a1a5e16216c..eaf31ac38efbb 100644
--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -140,6 +140,11 @@ static struct hrtimer_cpu_base migration_cpu_base = {
 
 #define migration_base	migration_cpu_base.clock_base[0]
 
+static bool is_migration_base(struct hrtimer_clock_base *base)
+{
+	return base == &migration_base;
+}
+
 /*
  * We are using hashed locking: holding per_cpu(hrtimer_bases)[n].lock
  * means that all timers which are tied to this base via timer->base are
@@ -264,6 +269,11 @@ switch_hrtimer_base(struct hrtimer *timer, struct hrtimer_clock_base *base,
 
 #else /* CONFIG_SMP */
 
+static bool is_migration_base(struct hrtimer_clock_base *base)
+{
+	return false;
+}
+
 static inline struct hrtimer_clock_base *
 lock_hrtimer_base(const struct hrtimer *timer, unsigned long *flags)
 {
@@ -1221,7 +1231,7 @@ void hrtimer_cancel_wait_running(const struct hrtimer *timer)
 	 * Just relax if the timer expires in hard interrupt context or if
 	 * it is currently on the migration base.
 	 */
-	if (!timer->is_soft || base == &migration_base)
+	if (!timer->is_soft || is_migration_base(base)) {
 		cpu_relax();
 		return;
 	}
-- 
2.23.0