From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Wed, 28 Mar 2018 11:15:19 +0200
Subject: posix-timers: move the rcu head out of the union
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git
Git-commit: b8401365af110949f12c7cf1fa86b4c0ea069bbd
Patch-mainline: Queued in subsystem maintainer repository
References: SLE Realtime Extension

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-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Mike Galbraith <mgalbraith@suse.de>
---
 include/linux/posix-timers.h |    2 +-
 kernel/time/posix-timers.c   |    4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

--- a/include/linux/posix-timers.h
+++ b/include/linux/posix-timers.h
@@ -82,8 +82,8 @@ struct k_itimer {
 			struct alarm alarmtimer;
 			ktime_t interval;
 		} alarm;
-		struct rcu_head rcu;
 	} it;
+	struct rcu_head rcu;
 };
 
 struct k_clock {
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -564,7 +564,7 @@ static struct k_itimer * alloc_posix_tim
 
 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);
 }
@@ -581,7 +581,7 @@ static void release_posix_timer(struct k
 	}
 	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)