btrfs: Push mnt_want_write() outside of i_mutex

When mnt_want_write() starts to handle freezing it will get a full lock
semantics requiring proper lock ordering. So push mnt_want_write() call
consistently outside of i_mutex.

CC: Chris Mason <chris.mason@oracle.com>
CC: linux-btrfs@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 11 insertions, 12 deletions

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 1e9f6c019ad0..cd93eb530b74 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -193,6 +193,10 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
         if (!inode_owner_or_capable(inode))
                 return -EACCES;
 
+        ret = mnt_want_write_file(file);
+        if (ret)
+                return ret;
+
         mutex_lock(&inode->i_mutex);
 
         ip_oldflags = ip->flags;
@@ -207,10 +211,6 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
                 }
         }
 
-        ret = mnt_want_write_file(file);
-        if (ret)
-                goto out_unlock;
-
         if (flags & FS_SYNC_FL)
                 ip->flags |= BTRFS_INODE_SYNC;
         else
@@ -273,9 +273,9 @@ static int btrfs_ioctl_setflags(struct file *file, void __user *arg)
                 inode->i_flags = i_oldflags;
         }
 
-        mnt_drop_write_file(file);
  out_unlock:
         mutex_unlock(&inode->i_mutex);
+        mnt_drop_write_file(file);
         return ret;
 }
 
@@ -641,6 +641,10 @@ static noinline int btrfs_mksubvol(struct path *parent,
         struct dentry *dentry;
         int error;
 
+        error = mnt_want_write(parent->mnt);
+        if (error)
+                return error;
+
         mutex_lock_nested(&dir->i_mutex, I_MUTEX_PARENT);
 
         dentry = lookup_one_len(name, parent->dentry, namelen);
@@ -652,13 +656,9 @@ static noinline int btrfs_mksubvol(struct path *parent,
         if (dentry->d_inode)
                 goto out_dput;
 
-        error = mnt_want_write(parent->mnt);
-        if (error)
-                goto out_dput;
-
         error = btrfs_may_create(dir, dentry);
         if (error)
-                goto out_drop_write;
+                goto out_dput;
 
         down_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
 
@@ -676,12 +676,11 @@ static noinline int btrfs_mksubvol(struct path *parent,
                 fsnotify_mkdir(dir, dentry);
 out_up_read:
         up_read(&BTRFS_I(dir)->root->fs_info->subvol_sem);
-out_drop_write:
-        mnt_drop_write(parent->mnt);
 out_dput:
         dput(dentry);
 out_unlock:
         mutex_unlock(&dir->i_mutex);
+        mnt_drop_write(parent->mnt);
         return error;
 }