1 files changed, 17 insertions, 8 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 1a9232356ef9..d8924bfaa9db 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2513,20 +2513,29 @@ void put_mnt_ns(struct mnt_namespace *ns)
 {
         struct vfsmount *root;
         LIST_HEAD(umount_list);
-        spinlock_t *lock;
 
-        lock = &get_cpu_var(vfsmount_lock);
-        if (!atomic_dec_and_lock(&ns->count, lock)) {
-                put_cpu_var(vfsmount_lock);
+        /*
+         * We open code this to avoid vfsmount_write_lock() in case of
+         * ns->count > 1
+         */
+        if (atomic_add_unless(&ns->count, -1, 1))
+                return;
+
+        /*
+         * Do the full locking here as it's likely that ns->count will
+         * drop to zero and we have to take namespace_sem and all vfs
+         * mount locks anyway for umount_tree().
+         */
+        down_write(&namespace_sem);
+        vfsmount_write_lock();
+        if (!atomic_dec_and_test(&ns->count)) {
+                vfsmount_write_unlock();
+                up_write(&namespace_sem);
                 return;
         }
         root = ns->root;
         ns->root = NULL;
-        spin_unlock(lock);
-        put_cpu_var(vfsmount_lock);
 
-        down_write(&namespace_sem);
-        vfsmount_write_lock();
         umount_tree(root, 0, &umount_list);
         vfsmount_write_unlock();
         up_write(&namespace_sem);