On RT the timer can be preempted while running and therefore we wait with timer_wait_for_callback() for the timer to complete (instead of busy looping). The RCU-readlock is held to ensure that this posix timer is not removed while we wait on it. If the timer is removed then it invokes call_rcu() with a pointer that is shared with the hrtimer because it is part of the same union. In order to avoid any possible side effects I am moving the rcu pointer out of the union.
Cc: [email protected] Signed-off-by: Sebastian Andrzej Siewior <[email protected]> --- v1…v2: add the lost hunk in posix-timers.c include/linux/posix-timers.h | 2 +- kernel/time/posix-timers.c | 4 ++-- 2 files changed, 3 insertions(+), 3 deletions(-) diff --git a/include/linux/posix-timers.h b/include/linux/posix-timers.h index 672c4f32311e..4754eb4298b1 100644 --- a/include/linux/posix-timers.h +++ b/include/linux/posix-timers.h @@ -101,8 +101,8 @@ struct k_itimer { struct { struct alarm alarmtimer; } alarm; - struct rcu_head rcu; } it; + struct rcu_head rcu; }; void run_posix_cpu_timers(struct task_struct *task); diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c index 3abd449a926f..17d4eb49e7c3 100644 --- a/kernel/time/posix-timers.c +++ b/kernel/time/posix-timers.c @@ -470,7 +470,7 @@ static struct k_itimer * alloc_posix_timer(void) static void k_itimer_rcu_free(struct rcu_head *head) { - struct k_itimer *tmr = container_of(head, struct k_itimer, it.rcu); + struct k_itimer *tmr = container_of(head, struct k_itimer, rcu); kmem_cache_free(posix_timers_cache, tmr); } @@ -487,7 +487,7 @@ static void release_posix_timer(struct k_itimer *tmr, int it_id_set) } put_pid(tmr->it_pid); sigqueue_free(tmr->sigq); - call_rcu(&tmr->it.rcu, k_itimer_rcu_free); + call_rcu(&tmr->rcu, k_itimer_rcu_free); } static int common_timer_create(struct k_itimer *new_timer) -- 2.16.3
