skip permission checks for extended attributes

zfs_zaccess_trivial() calls the generic_permission() to read
xattr attributes. This causes deadlock if called from
zpl_xattr_set_dir() context as xattr and the dent locks are
already held in this scenario. This commit skips the permissions
checks for extended attributes since the Linux VFS stack already
checks it before passing us the control.

Signed-off-by: Ameer Hamza <ahamza@ixsystems.com>

module/os/linux/zfs/zfs_dir.c

@@ -1066,9 +1066,6 @@ zfs_make_xattrdir(znode_t *zp, vattr_t *vap, znode_t **xzpp, cred_t *cr)
 
 	*xzpp = NULL;
 
-	if ((error = zfs_zaccess(zp, ACE_WRITE_NAMED_ATTRS, 0, B_FALSE, cr)))
-		return (error);
-
 	if ((error = zfs_acl_ids_create(zp, IS_XATTR, vap, cr, NULL,
 	    &acl_ids)) != 0)
 		return (error);

module/os/linux/zfs/zfs_vnops_os.c

@@ -579,6 +579,7 @@ zfs_create(znode_t *dzp, char *name, vattr_t *vap, int excl,
 	boolean_t	fuid_dirtied;
 	boolean_t	have_acl = B_FALSE;
 	boolean_t	waited = B_FALSE;
+	boolean_t	skip_acl = (flag & ATTR_NOACLCHECK) ? B_TRUE : B_FALSE;
 
 	/*
 	 * If we have an ephemeral id, ACL, or XVATTR then
@@ -651,7 +652,7 @@ top:
 		 * Create a new file object and update the directory
 		 * to reference it.
 		 */
-		if ((error = zfs_zaccess(dzp, ACE_ADD_FILE, 0, B_FALSE, cr))) {
+		if ((error = zfs_zaccess(dzp, ACE_ADD_FILE, 0, skip_acl, cr))) {
 			if (have_acl)
 				zfs_acl_ids_free(&acl_ids);
 			goto out;

module/os/linux/zfs/zpl_xattr.c

@@ -496,7 +496,7 @@ zpl_xattr_set_dir(struct inode *ip, const char *name, const void *value,
 		vap->va_gid = crgetgid(cr);
 
 		error = -zfs_create(dxzp, (char *)name, vap, 0, 0644, &xzp,
-		    cr, 0, NULL);
+		    cr, ATTR_NOACLCHECK, NULL);
 		if (error)
 			goto out;
 	}