pull mnt_want_write()/mnt_drop_write() into kern_path_create()/done_path_create() resp.

One side effect - attempt to create a cross-device link on a read-only fs fails
with EROFS instead of EXDEV now.  Makes more sense, POSIX allows, etc.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 18 insertions, 50 deletions

diff --git a/fs/namei.c b/fs/namei.c
index cf362dc9d1fd..a3fb78fd70d2 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2865,10 +2865,11 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
         mutex_lock_nested(&nd.path.dentry->d_inode->i_mutex, I_MUTEX_PARENT);
         dentry = lookup_hash(&nd);
         if (IS_ERR(dentry))
-                goto fail;
+                goto unlock;
 
+        error = -EEXIST;
         if (dentry->d_inode)
-                goto eexist;
+                goto fail;
         /*
          * Special case - lookup gave negative, but... we had foo/bar/
          * From the vfs_mknod() POV we just have a negative dentry -
@@ -2876,16 +2877,18 @@ struct dentry *kern_path_create(int dfd, const char *pathname, struct path *path
          * been asking for (non-existent) directory. -ENOENT for you.
          */
         if (unlikely(!is_dir && nd.last.name[nd.last.len])) {
-                dput(dentry);
-                dentry = ERR_PTR(-ENOENT);
+                error = -ENOENT;
                 goto fail;
         }
+        error = mnt_want_write(nd.path.mnt);
+        if (error)
+                goto fail;
         *path = nd.path;
         return dentry;
-eexist:
-        dput(dentry);
-        dentry = ERR_PTR(-EEXIST);
 fail:
+        dput(dentry);
+        dentry = ERR_PTR(error);
+unlock:
         mutex_unlock(&nd.path.dentry->d_inode->i_mutex);
 out:
         path_put(&nd.path);
@@ -2897,6 +2900,7 @@ void done_path_create(struct path *path, struct dentry *dentry)
 {
         dput(dentry);
         mutex_unlock(&path->dentry->d_inode->i_mutex);
+        mnt_drop_write(path->mnt);
         path_put(path);
 }
 EXPORT_SYMBOL(done_path_create);
@@ -2974,12 +2978,9 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
 
         if (!IS_POSIXACL(path.dentry->d_inode))
                 mode &= ~current_umask();
-        error = mnt_want_write(path.mnt);
-        if (error)
-                goto out_dput;
         error = security_path_mknod(&path, dentry, mode, dev);
         if (error)
-                goto out_drop_write;
+                goto out;
         switch (mode & S_IFMT) {
                 case 0: case S_IFREG:
                         error = vfs_create(path.dentry->d_inode,dentry,mode,true);
@@ -2992,11 +2993,8 @@ SYSCALL_DEFINE4(mknodat, int, dfd, const char __user *, filename, umode_t, mode,
                         error = vfs_mknod(path.dentry->d_inode,dentry,mode,0);
                         break;
         }
-out_drop_write:
-        mnt_drop_write(path.mnt);
-out_dput:
+out:
         done_path_create(&path, dentry);
-
         return error;
 }
 
@@ -3042,16 +3040,9 @@ SYSCALL_DEFINE3(mkdirat, int, dfd, const char __user *, pathname, umode_t, mode)
 
         if (!IS_POSIXACL(path.dentry->d_inode))
                 mode &= ~current_umask();
-        error = mnt_want_write(path.mnt);
-        if (error)
-                goto out_dput;
         error = security_path_mkdir(&path, dentry, mode);
-        if (error)
-                goto out_drop_write;
-        error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
-out_drop_write:
-        mnt_drop_write(path.mnt);
-out_dput:
+        if (!error)
+                error = vfs_mkdir(path.dentry->d_inode, dentry, mode);
         done_path_create(&path, dentry);
         return error;
 }
@@ -3326,16 +3317,9 @@ SYSCALL_DEFINE3(symlinkat, const char __user *, oldname,
         if (IS_ERR(dentry))
                 goto out_putname;
 
-        error = mnt_want_write(path.mnt);
-        if (error)
-                goto out_dput;
         error = security_path_symlink(&path, dentry, from);
-        if (error)
-                goto out_drop_write;
-        error = vfs_symlink(path.dentry->d_inode, dentry, from);
-out_drop_write:
-        mnt_drop_write(path.mnt);
-out_dput:
+        if (!error)
+                error = vfs_symlink(path.dentry->d_inode, dentry, from);
         done_path_create(&path, dentry);
 out_putname:
         putname(from);
@@ -3436,15 +3420,10 @@ SYSCALL_DEFINE5(linkat, int, olddfd, const char __user *, oldname,
         error = -EXDEV;
         if (old_path.mnt != new_path.mnt)
                 goto out_dput;
-        error = mnt_want_write(new_path.mnt);
-        if (error)
-                goto out_dput;
         error = security_path_link(old_path.dentry, &new_path, new_dentry);
         if (error)
-                goto out_drop_write;
+                goto out_dput;
         error = vfs_link(old_path.dentry, new_path.dentry->d_inode, new_dentry);
-out_drop_write:
-        mnt_drop_write(new_path.mnt);
 out_dput:
         done_path_create(&new_path, new_dentry);
 out:
diff --git a/fs/ocfs2/refcounttree.c b/fs/ocfs2/refcounttree.c
index 23cf78f68503..30a055049e16 100644
--- a/fs/ocfs2/refcounttree.c
+++ b/fs/ocfs2/refcounttree.c
@@ -4466,16 +4466,9 @@ int ocfs2_reflink_ioctl(struct inode *inode,
                 goto out_dput;
         }
 
-        error = mnt_want_write(new_path.mnt);
-        if (error) {
-                mlog_errno(error);
-                goto out_dput;
-        }
-
         error = ocfs2_vfs_reflink(old_path.dentry,
                                   new_path.dentry->d_inode,
                                   new_dentry, preserve);
-        mnt_drop_write(new_path.mnt);
 out_dput:
         done_path_create(&new_path, new_dentry);
 out:
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e8239540683a..88ab72820b9f 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -876,15 +876,11 @@ static int unix_bind(struct socket *sock, struct sockaddr *uaddr, int addr_len)
                  */
                 mode = S_IFSOCK |
                        (SOCK_INODE(sock)->i_mode & ~current_umask());
-                err = mnt_want_write(path.mnt);
-                if (err)
-                        goto out_mknod_dput;
                 err = security_path_mknod(&path, dentry, mode, 0);
                 if (err)
                         goto out_mknod_drop_write;
                 err = vfs_mknod(path.dentry->d_inode, dentry, mode, 0);
 out_mknod_drop_write:
-                mnt_drop_write(path.mnt);
                 if (err)
                         goto out_mknod_dput;
                 mntget(path.mnt);