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Subject[PATCH RT 2/3] posix-timers: move the rcu head out of the union
Date
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

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>
---
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 907f3fd191ac..e2e43c61f6a1 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 48ca053dae2e..0808e2ae49bf 100644
--- a/kernel/time/posix-timers.c
+++ b/kernel/time/posix-timers.c
@@ -567,7 +567,7 @@ 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);
}
@@ -584,7 +584,7 @@ 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)
--
2.14.3
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