[PATCH 3/4] rtmutex: Add rt_mutex_init_waiter helper

[Davidlohr Bueso]

... encapsulates debug and regular waiter initialization. In the
case of rtmutexes, we now also set the waiter to nil until later
explicitly set to whatever task instead of the magic number. This
is safe as the waiter is on he stack and we are doing very basic
initialization anyway.

Signed-off-by: Davidlohr Bueso <dbueso@xxxxxxx>
---
 kernel/futex.c                  |  5 +----
 kernel/locking/rtmutex.c        |  4 +---
 kernel/locking/rtmutex_common.h | 15 +++++++++++++++
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index a5d2e74c89e0..d4e0da984741 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -2782,10 +2782,7 @@ static int futex_wait_requeue_pi(u32 __user *uaddr, unsigned int flags,
 	 * The waiter is allocated on our stack, manipulated by the requeue
 	 * code while we sleep on uaddr.
 	 */
-	debug_rt_mutex_init_waiter(&rt_waiter);
-	RB_CLEAR_NODE(&rt_waiter.pi_tree_entry);
-	RB_CLEAR_NODE(&rt_waiter.tree_entry);
-	rt_waiter.task = NULL;
+	rt_mutex_init_waiter(&rt_waiter);
 
 	ret = get_futex_key(uaddr2, flags & FLAGS_SHARED, &key2, VERIFY_WRITE);
 	if (unlikely(ret != 0))
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 3e746607abe5..60fa79ae6d99 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -1171,9 +1171,7 @@ rt_mutex_slowlock(struct rt_mutex *lock, int state,
 	unsigned long flags;
 	int ret = 0;
 
-	debug_rt_mutex_init_waiter(&waiter);
-	RB_CLEAR_NODE(&waiter.pi_tree_entry);
-	RB_CLEAR_NODE(&waiter.tree_entry);
+	rt_mutex_init_waiter(&waiter);
 
 	/*
 	 * Technically we could use raw_spin_[un]lock_irq() here, but this can
diff --git a/kernel/locking/rtmutex_common.h b/kernel/locking/rtmutex_common.h
index 4f5f83c7d2d3..c7147376324e 100644
--- a/kernel/locking/rtmutex_common.h
+++ b/kernel/locking/rtmutex_common.h
@@ -119,4 +119,19 @@ extern void rt_mutex_adjust_prio(struct task_struct *task);
 # include "rtmutex.h"
 #endif
 
+/*
+ * Waiter structure basic initialization. A waiter is not considered
+ * actually usable until it after calling task_blocks_on_rt_mutex()
+ * which setups up the relevant entries.
+ */
+static inline void
+rt_mutex_init_waiter(struct rt_mutex_waiter *waiter)
+{
+       debug_rt_mutex_init_waiter(waiter);
+
+       RB_CLEAR_NODE(&waiter->pi_tree_entry);
+       RB_CLEAR_NODE(&waiter->tree_entry);
+       waiter->task = NULL;
+}
+
 #endif
-- 
2.7.4