4 files changed, 8 insertions, 2 deletions

diff --git a/fs/nilfs2/ioctl.c b/fs/nilfs2/ioctl.c
index 06658caa18bd..0b6387c67e6c 100644
--- a/fs/nilfs2/ioctl.c
+++ b/fs/nilfs2/ioctl.c
@@ -182,7 +182,7 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
         if (copy_from_user(&cpmode, argp, sizeof(cpmode)))
                 goto out;
 
-        down_read(&inode->i_sb->s_umount);
+        mutex_lock(&nilfs->ns_snapshot_mount_mutex);
 
         nilfs_transaction_begin(inode->i_sb, &ti, 0);
         ret = nilfs_cpfile_change_cpmode(
@@ -192,7 +192,7 @@ static int nilfs_ioctl_change_cpmode(struct inode *inode, struct file *filp,
         else
                 nilfs_transaction_commit(inode->i_sb); /* never fails */
 
-        up_read(&inode->i_sb->s_umount);
+        mutex_unlock(&nilfs->ns_snapshot_mount_mutex);
 out:
         mnt_drop_write_file(filp);
         return ret;
diff --git a/fs/nilfs2/super.c b/fs/nilfs2/super.c
index a76d6ea51ffb..6522cac6057c 100644
--- a/fs/nilfs2/super.c
+++ b/fs/nilfs2/super.c
@@ -945,6 +945,8 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
         struct nilfs_root *root;
         int ret;
 
+        mutex_lock(&nilfs->ns_snapshot_mount_mutex);
+
         down_read(&nilfs->ns_segctor_sem);
         ret = nilfs_cpfile_is_snapshot(nilfs->ns_cpfile, cno);
         up_read(&nilfs->ns_segctor_sem);
@@ -969,6 +971,7 @@ static int nilfs_attach_snapshot(struct super_block *s, __u64 cno,
         ret = nilfs_get_root_dentry(s, root, root_dentry);
         nilfs_put_root(root);
  out:
+        mutex_unlock(&nilfs->ns_snapshot_mount_mutex);
         return ret;
 }
 
diff --git a/fs/nilfs2/the_nilfs.c b/fs/nilfs2/the_nilfs.c
index 501b7f8b739f..41e6a04a561f 100644
--- a/fs/nilfs2/the_nilfs.c
+++ b/fs/nilfs2/the_nilfs.c
@@ -76,6 +76,7 @@ struct the_nilfs *alloc_nilfs(struct block_device *bdev)
         nilfs->ns_bdev = bdev;
         atomic_set(&nilfs->ns_ndirtyblks, 0);
         init_rwsem(&nilfs->ns_sem);
+        mutex_init(&nilfs->ns_snapshot_mount_mutex);
         INIT_LIST_HEAD(&nilfs->ns_dirty_files);
         INIT_LIST_HEAD(&nilfs->ns_gc_inodes);
         spin_lock_init(&nilfs->ns_inode_lock);
diff --git a/fs/nilfs2/the_nilfs.h b/fs/nilfs2/the_nilfs.h
index ef40a510e2f3..2558f320b821 100644
--- a/fs/nilfs2/the_nilfs.h
+++ b/fs/nilfs2/the_nilfs.h
@@ -47,6 +47,7 @@ enum {
  * @ns_flags: flags
  * @ns_bdev: block device
  * @ns_sem: semaphore for shared states
+ * @ns_snapshot_mount_mutex: mutex to protect snapshot mounts
  * @ns_sbh: buffer heads of on-disk super blocks
  * @ns_sbp: pointers to super block data
  * @ns_sbwtime: previous write time of super block
@@ -100,6 +101,7 @@ struct the_nilfs {
 
         struct block_device    *ns_bdev;
         struct rw_semaphore     ns_sem;
+        struct mutex            ns_snapshot_mount_mutex;
 
         /*
          * used for