futex: Cleanup refcounting

Add a put_pit_state() as counterpart for get_pi_state() so the refcounting
becomes consistent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: dvhart@infradead.org
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170322104151.801778516@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 9 insertions, 4 deletions

diff --git a/kernel/futex.c b/kernel/futex.c
index 3e71d66cb788..3b6dbeecd91b 100644
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -802,7 +802,7 @@ static int refill_pi_state_cache(void)
         return 0;
 }
 
-static struct futex_pi_state * alloc_pi_state(void)
+static struct futex_pi_state *alloc_pi_state(void)
 {
         struct futex_pi_state *pi_state = current->pi_state_cache;
 
@@ -812,6 +812,11 @@ static struct futex_pi_state * alloc_pi_state(void)
         return pi_state;
 }
 
+static void get_pi_state(struct futex_pi_state *pi_state)
+{
+        WARN_ON_ONCE(!atomic_inc_not_zero(&pi_state->refcount));
+}
+
 /*
  * Drops a reference to the pi_state object and frees or caches it
  * when the last reference is gone.
@@ -856,7 +861,7 @@ static void put_pi_state(struct futex_pi_state *pi_state)
  * Look up the task based on what TID userspace gave us.
  * We dont trust it.
  */
-static struct task_struct * futex_find_get_task(pid_t pid)
+static struct task_struct *futex_find_get_task(pid_t pid)
 {
         struct task_struct *p;
 
@@ -1103,7 +1108,7 @@ static int attach_to_pi_state(u32 __user *uaddr, u32 uval,
                 goto out_einval;
 
 out_attach:
-        atomic_inc(&pi_state->refcount);
+        get_pi_state(pi_state);
         raw_spin_unlock_irq(&pi_state->pi_mutex.wait_lock);
         *ps = pi_state;
         return 0;
@@ -1990,7 +1995,7 @@ retry_private:
                          * refcount on the pi_state and store the pointer in
                          * the futex_q object of the waiter.
                          */
-                        atomic_inc(&pi_state->refcount);
+                        get_pi_state(pi_state);
                         this->pi_state = pi_state;
                         ret = rt_mutex_start_proxy_lock(&pi_state->pi_mutex,
                                                         this->rt_waiter,