NFS: Fix a umount race

Ensure that we unregister the bdi before kill_anon_super() calls
ida_remove() on our device name.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: stable@kernel.org

1 files changed, 14 insertions, 1 deletions

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index ce907efc5508..f1afee4eea77 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -243,6 +243,7 @@ static int  nfs_show_stats(struct seq_file *, struct vfsmount *);
 static int nfs_get_sb(struct file_system_type *, int, const char *, void *, struct vfsmount *);
 static int nfs_xdev_get_sb(struct file_system_type *fs_type,
                 int flags, const char *dev_name, void *raw_data, struct vfsmount *mnt);
+static void nfs_put_super(struct super_block *);
 static void nfs_kill_super(struct super_block *);
 static int nfs_remount(struct super_block *sb, int *flags, char *raw_data);
 
@@ -266,6 +267,7 @@ static const struct super_operations nfs_sops = {
         .alloc_inode    = nfs_alloc_inode,
         .destroy_inode  = nfs_destroy_inode,
         .write_inode    = nfs_write_inode,
+        .put_super      = nfs_put_super,
         .statfs         = nfs_statfs,
         .clear_inode    = nfs_clear_inode,
         .umount_begin   = nfs_umount_begin,
@@ -335,6 +337,7 @@ static const struct super_operations nfs4_sops = {
         .alloc_inode    = nfs_alloc_inode,
         .destroy_inode  = nfs_destroy_inode,
         .write_inode    = nfs_write_inode,
+        .put_super      = nfs_put_super,
         .statfs         = nfs_statfs,
         .clear_inode    = nfs4_clear_inode,
         .umount_begin   = nfs_umount_begin,
@@ -2258,6 +2261,17 @@ error_splat_super:
 }
 
 /*
+ * Ensure that we unregister the bdi before kill_anon_super
+ * releases the device name
+ */
+static void nfs_put_super(struct super_block *s)
+{
+        struct nfs_server *server = NFS_SB(s);
+
+        bdi_unregister(&server->backing_dev_info);
+}
+
+/*
  * Destroy an NFS2/3 superblock
  */
 static void nfs_kill_super(struct super_block *s)
@@ -2265,7 +2279,6 @@ static void nfs_kill_super(struct super_block *s)
         struct nfs_server *server = NFS_SB(s);
 
         kill_anon_super(s);
-        bdi_unregister(&server->backing_dev_info);
         nfs_fscache_release_super_cookie(s);
         nfs_free_server(server);
 }