From: Thomas Gleixner Date: Wed, 20 Dec 2017 17:12:51 +0100 Subject: [PATCH 02/29] hrtimer: Correct blantanly wrong comment Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.14/older/patches-4.14.15-rt13.tar.xz The protection of a hrtimer which runs its callback against migration to a different CPU has nothing to do with hard interrupt context. The protection against migration of a hrtimer running the expiry callback is the pointer in the cpu_base which holds a pointer to the currently running timer. This pointer is evaluated in the code which potentially switches the timer base and makes sure it's kept on the CPU on which the callback is running. Reported-by: Anna-Maria Gleixner Signed-off-by: Thomas Gleixner Signed-off-by: Anna-Maria Gleixner Signed-off-by: Sebastian Andrzej Siewior --- kernel/time/hrtimer.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/kernel/time/hrtimer.c +++ b/kernel/time/hrtimer.c @@ -1197,9 +1197,9 @@ static void __run_hrtimer(struct hrtimer timer->is_rel = false; /* - * Because we run timers from hardirq context, there is no chance - * they get migrated to another cpu, therefore its safe to unlock - * the timer base. + * The timer is marked as running in the cpu base, so it is + * protected against migration to a different CPU even if the lock + * is dropped. */ raw_spin_unlock(&cpu_base->lock); trace_hrtimer_expire_entry(timer, now);