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>

diff --git a/kernel/futex.c b/kernel/futex.c
index 3e71d66cb78814a3bd41452bcc2d5cc2e5662b24..3b6dbeecd91be431eea601ed9d458f00b2d4a68b 100644 (file)
--- 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,