[PATCH RT 18/22] posix-timers: move the rcu head out of the union

[Julia Cartwright]

From: Sebastian Andrzej Siewior <bige...@linutronix.de>

4.9.115-rt94-rc1 stable review patch.
If you have any objection to the inclusion of this patch, let me know.

--- 8< --- 8< --- 8< ---
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: stable...@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de>
(cherry picked from commit b8401365af110949f12c7cf1fa86b4c0ea069bbd)
Signed-off-by: Julia Cartwright <ju...@ni.com>
---
 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 62d44c176071..cbd3f9334543 100644
--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -92,8 +92,8 @@ struct k_itimer {
                        struct alarm alarmtimer;
                        ktime_t interval;
                } alarm;
-               struct rcu_head rcu;
        } it;
+       struct rcu_head         rcu;
 };
 
 struct k_clock {
diff --git a/kernel/time/posix-timers.c b/kernel/time/posix-timers.c
index 6084618436fd..45d8033caec4 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -568,7 +568,7 @@ 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);
 }
@@ -585,7 +585,7 @@ 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 struct k_clock *clockid_to_kclock(const clockid_t id)
-- 
2.18.0