dlm: prevent NPD when writing a positive value to event_done

do_uevent returns the value written to event_done. In case it is a
positive value, new_lockspace would undo all the work, and lockspace
would not be set. __dlm_new_lockspace, however, would treat that
positive value as a success due to commit 8511a27 ("dlm: fix use
count with multiple joins").

Down the line, device_create_lockspace would pass that NULL lockspace to
dlm_find_lockspace_local, leading to a NULL pointer dereference.

Treating such positive values as successes prevents the problem. Given
this has been broken for so long, this is unlikely to break userspace
expectations.

Fixes: 8511a27 ("dlm: fix use count with multiple joins")
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com>
Signed-off-by: David Teigland <teigland@redhat.com>

Author: Thadeu Lima de Souza Cascardo

fs/dlm/lockspace.c

@@ -576,7 +576,7 @@ static int new_lockspace(const char *name, const char *cluster,
 	   lockspace to start running (via sysfs) in dlm_ls_start(). */
 
 	error = do_uevent(ls, 1);
-	if (error)
+	if (error < 0)
 		goto out_recoverd;
 
 	/* wait until recovery is successful or failed */