[PATCH 6/8] unix_bind_bsd(): move done_path_create() call after dealing with ->bindlock

[Al Viro]

Final preparations for doing unlink on failure past the successful
mknod.  We can't hold ->bindlock over ->mknod() or ->unlink(), since
either might do sb_start_write() (e.g. on overlayfs).  However, we
can do it while holding filesystem and VFS locks - doing
        kern_path_create()
        vfs_mknod()
        grab ->bindlock
        if u->addr had been set
                drop ->bindlock
                done_path_create
                return -EINVAL
        else
                assign the address to socket
                drop ->bindlock
                done_path_create
                return 0
would be deadlock-free.  Here we massage unix_bind_bsd() to that
form.  We are still doing equivalent transformations.

Next commit will *not* be an equivalent transformation - it will
add a call of vfs_unlink() before done_path_create() in "alread bound"
case.

Signed-off-by: Al Viro <v...@zeniv.linux.org.uk>
---
 net/unix/af_unix.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 5e04e16e6b88..368376621111 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -988,7 +988,7 @@ static int unix_bind_bsd(struct sock *sk, struct 
unix_address *addr)
        struct unix_sock *u = unix_sk(sk);
        umode_t mode = S_IFSOCK |
               (SOCK_INODE(sk->sk_socket)->i_mode & ~current_umask());
-       struct path parent, path;
+       struct path parent;
        struct dentry *dentry;
        unsigned int hash;
        int err;
@@ -1005,36 +1005,32 @@ static int unix_bind_bsd(struct sock *sk, struct 
unix_address *addr)
         * All right, let's create it.
         */
        err = security_path_mknod(&parent, dentry, mode, 0);
-       if (!err) {
+       if (!err)
                err = vfs_mknod(d_inode(parent.dentry), dentry, mode, 0);
-               if (!err) {
-                       path.mnt = mntget(parent.mnt);
-                       path.dentry = dget(dentry);
-               }
-       }
-       done_path_create(&parent, dentry);
-       if (err)
+       if (err) {
+               done_path_create(&parent, dentry);
                return err;
-
+       }
        err = mutex_lock_interruptible(&u->bindlock);
        if (err) {
-               path_put(&path);
+               done_path_create(&parent, dentry);
                return err;
        }
-
        if (u->addr) {
                mutex_unlock(&u->bindlock);
-               path_put(&path);
+               done_path_create(&parent, dentry);
                return -EINVAL;
        }
 
        addr->hash = UNIX_HASH_SIZE;
-       hash = d_backing_inode(path.dentry)->i_ino & (UNIX_HASH_SIZE - 1);
+       hash = d_backing_inode(dentry)->i_ino & (UNIX_HASH_SIZE - 1);
        spin_lock(&unix_table_lock);
-       u->path = path;
+       u->path.mnt = mntget(parent.mnt);
+       u->path.dentry = dget(dentry);
        __unix_set_addr(sk, addr, hash);
        spin_unlock(&unix_table_lock);
        mutex_unlock(&u->bindlock);
+       done_path_create(&parent, dentry);
        return 0;
 }
 
-- 
2.11.0