vfs: take i_mutex on renamed file

A read delegation is used by NFSv4 as a guarantee that a client can
perform local read opens without informing the server.

The open operation takes the last component of the pathname as an
argument, thus is also a lookup operation, and giving the client the
above guarantee means informing the client before we allow anything that
would change the set of names pointing to the inode.

Therefore, we need to break delegations on rename, link, and unlink.

We also need to prevent new delegations from being acquired while one of
these operations is in progress.

We could add some completely new locking for that purpose, but it's
simpler to use the i_mutex, since that's already taken by all the
operations we care about.

The single exception is rename.  So, modify rename to take the i_mutex
on the file that is being renamed.

Also fix up lockdep and Documentation/filesystems/directory-locking to
reflect the change.

Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 5 insertions, 5 deletions

diff --git a/fs/namei.c b/fs/namei.c
index 2a5a7aa9f43f..88cec0330bf7 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -3918,7 +3918,8 @@ SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname
  *         That's where 4.4 screws up. Current fix: serialization on
  *         sb->s_vfs_rename_mutex. We might be more accurate, but that's another
  *         story.
- *      c) we have to lock _three_ objects - parents and victim (if it exists).
+ *      c) we have to lock _four_ objects - parents and victim (if it exists),
+ *         and source (if it is not a directory).
  *         And that - after we got ->i_mutex on parents (until then we don't know
  *         whether the target exists).  Solution: try to be smart with locking
  *         order for inodes.  We rely on the fact that tree topology may change
@@ -3994,6 +3995,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
                             struct inode *new_dir, struct dentry *new_dentry)
 {
         struct inode *target = new_dentry->d_inode;
+        struct inode *source = old_dentry->d_inode;
         int error;
 
         error = security_inode_rename(old_dir, old_dentry, new_dir, new_dentry);
@@ -4001,8 +4003,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
                 return error;
 
         dget(new_dentry);
-        if (target)
-                mutex_lock(&target->i_mutex);
+        lock_two_nondirectories(source, target);
 
         error = -EBUSY;
         if (d_mountpoint(old_dentry)||d_mountpoint(new_dentry))
@@ -4017,8 +4018,7 @@ static int vfs_rename_other(struct inode *old_dir, struct dentry *old_dentry,
         if (!(old_dir->i_sb->s_type->fs_flags & FS_RENAME_DOES_D_MOVE))
                 d_move(old_dentry, new_dentry);
 out:
-        if (target)
-                mutex_unlock(&target->i_mutex);
+        unlock_two_nondirectories(source, target);
         dput(new_dentry);
         return error;
 }