3 files changed, 5 insertions, 3 deletions

diff --git a/fs/super.c b/fs/super.c
index 7e9dd4cc2c01..0d89e93f654e 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -71,6 +71,7 @@ static struct super_block *alloc_super(struct file_system_type *type)
 #else
                 INIT_LIST_HEAD(&s->s_files);
 #endif
+                s->s_bdi = &default_backing_dev_info;
                 INIT_LIST_HEAD(&s->s_instances);
                 INIT_HLIST_BL_HEAD(&s->s_anon);
                 INIT_LIST_HEAD(&s->s_inodes);
@@ -1003,6 +1004,7 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
         }
         BUG_ON(!mnt->mnt_sb);
         WARN_ON(!mnt->mnt_sb->s_bdi);
+        WARN_ON(mnt->mnt_sb->s_bdi == &default_backing_dev_info);
         mnt->mnt_sb->s_flags |= MS_BORN;
 
         error = security_sb_kern_mount(mnt->mnt_sb, flags, secdata);
diff --git a/fs/sync.c b/fs/sync.c
index ba76b9623e7e..412dc89163d3 100644
--- a/fs/sync.c
+++ b/fs/sync.c
@@ -33,7 +33,7 @@ static int __sync_filesystem(struct super_block *sb, int wait)
          * This should be safe, as we require bdi backing to actually
          * write out data in the first place
          */
-        if (!sb->s_bdi || sb->s_bdi == &noop_backing_dev_info)
+        if (sb->s_bdi == &noop_backing_dev_info)
                 return 0;
 
         if (sb->s_qcop && sb->s_qcop->quota_sync)
@@ -79,7 +79,7 @@ EXPORT_SYMBOL_GPL(sync_filesystem);
 
 static void sync_one_sb(struct super_block *sb, void *arg)
 {
-        if (!(sb->s_flags & MS_RDONLY) && sb->s_bdi)
+        if (!(sb->s_flags & MS_RDONLY))
                 __sync_filesystem(sb, *(int *)arg);
 }
 /*
diff --git a/mm/backing-dev.c b/mm/backing-dev.c
index c91e139a652e..8fe9d3407921 100644
--- a/mm/backing-dev.c
+++ b/mm/backing-dev.c
@@ -598,7 +598,7 @@ static void bdi_prune_sb(struct backing_dev_info *bdi)
         spin_lock(&sb_lock);
         list_for_each_entry(sb, &super_blocks, s_list) {
                 if (sb->s_bdi == bdi)
-                        sb->s_bdi = NULL;
+                        sb->s_bdi = &default_backing_dev_info;
         }
         spin_unlock(&sb_lock);
 }