locking/rwsem: Reinit wake_q after use

In __rwsem_down_write_failed_common(), the same wake_q variable name
is defined twice, with the inner wake_q hiding the one in outer scope.
We can either use different names for the two wake_q's.

Even better, we can use the same wake_q twice, if necessary.

To enable the latter change, we need to define a new helper function
wake_q_init() to enable reinitalization of wake_q after use.

Signed-off-by: Waiman Long <longman@redhat.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1485052415-9611-1-git-send-email-longman@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/include/linux/sched.h b/include/linux/sched.h
index f4f9d32..4e62b37 100644 (file)
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1021,6 +1021,12 @@ struct wake_q_head {
 #define DEFINE_WAKE_Q(name)                            \
        struct wake_q_head name = { WAKE_Q_TAIL, &name.first }
 
+static inline void wake_q_init(struct wake_q_head *head)
+{
+       head->first = WAKE_Q_TAIL;
+       head->lastp = &head->first;
+}
+
 extern void wake_q_add(struct wake_q_head *head,
                       struct task_struct *task);
 extern void wake_up_q(struct wake_q_head *head);

diff --git a/kernel/locking/rwsem-xadd.c b/kernel/locking/rwsem-xadd.c
index a3a381a..2ad8d8d 100644 (file)
--- a/kernel/locking/rwsem-xadd.c
+++ b/kernel/locking/rwsem-xadd.c
@@ -502,8 +502,6 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
                 * wake any read locks that were queued ahead of us.
                 */
                if (count > RWSEM_WAITING_BIAS) {
-                       DEFINE_WAKE_Q(wake_q);
-
                        __rwsem_mark_wake(sem, RWSEM_WAKE_READERS, &wake_q);
                        /*
                         * The wakeup is normally called _after_ the wait_lock
@@ -513,6 +511,11 @@ __rwsem_down_write_failed_common(struct rw_semaphore *sem, int state)
                         * for attempting rwsem_try_write_lock().
                         */
                        wake_up_q(&wake_q);
+
+                       /*
+                        * Reinitialize wake_q after use.
+                        */
+                       wake_q_init(&wake_q);
                }
 
        } else