1 files changed, 48 insertions, 6 deletions

diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index 50ef7d2ef03c..0c77bdc238b2 100644
--- a/fs/fs_pin.c
+++ b/fs/fs_pin.c
@@ -1,4 +1,5 @@
 #include <linux/fs.h>
+#include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/fs_pin.h>
 #include "internal.h"
@@ -12,6 +13,10 @@ void pin_remove(struct fs_pin *pin)
 	hlist_del(&pin->m_list);
 	hlist_del(&pin->s_list);
 	spin_unlock(&pin_lock);
+	spin_lock_irq(&pin->wait.lock);
+	pin->done = 1;
+	wake_up_locked(&pin->wait);
+	spin_unlock_irq(&pin->wait.lock);
 }
 
 void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
@@ -28,19 +33,58 @@ void pin_insert(struct fs_pin *pin, struct vfsmount *m)
 	pin_insert_group(pin, m, &m->mnt_sb->s_pins);
 }
 
+void pin_kill(struct fs_pin *p)
+{
+	wait_queue_t wait;
+
+	if (!p) {
+		rcu_read_unlock();
+		return;
+	}
+	init_wait(&wait);
+	spin_lock_irq(&p->wait.lock);
+	if (likely(!p->done)) {
+		p->done = -1;
+		spin_unlock_irq(&p->wait.lock);
+		rcu_read_unlock();
+		p->kill(p);
+		return;
+	}
+	if (p->done > 0) {
+		spin_unlock_irq(&p->wait.lock);
+		rcu_read_unlock();
+		return;
+	}
+	__add_wait_queue(&p->wait, &wait);
+	while (1) {
+		set_current_state(TASK_UNINTERRUPTIBLE);
+		spin_unlock_irq(&p->wait.lock);
+		rcu_read_unlock();
+		schedule();
+		rcu_read_lock();
+		if (likely(list_empty(&wait.task_list)))
+			break;
+		/* OK, we know p couldn't have been freed yet */
+		spin_lock_irq(&p->wait.lock);
+		if (p->done > 0) {
+			spin_unlock_irq(&p->wait.lock);
+			break;
+		}
+	}
+	rcu_read_unlock();
+}
+
 void mnt_pin_kill(struct mount *m)
 {
 	while (1) {
 		struct hlist_node *p;
-		struct fs_pin *pin;
 		rcu_read_lock();
 		p = ACCESS_ONCE(m->mnt_pins.first);
 		if (!p) {
 			rcu_read_unlock();
 			break;
 		}
-		pin = hlist_entry(p, struct fs_pin, m_list);
-		pin->kill(pin);
+		pin_kill(hlist_entry(p, struct fs_pin, m_list));
 	}
 }
 
@@ -48,14 +92,12 @@ void group_pin_kill(struct hlist_head *p)
 {
 	while (1) {
 		struct hlist_node *q;
-		struct fs_pin *pin;
 		rcu_read_lock();
 		q = ACCESS_ONCE(p->first);
 		if (!q) {
 			rcu_read_unlock();
 			break;
 		}
-		pin = hlist_entry(q, struct fs_pin, s_list);
-		pin->kill(pin);
+		pin_kill(hlist_entry(q, struct fs_pin, s_list));
 	}
 }