Prevent tsleep(9) with PCATCH from returning immediately without error

when called during execve(2). This was a caused by initializing sls_sig
with value 0 in r1.164 of kern_synch.c. Previously, tsleep(9) returned
immediately with EINTR in similar circumstances.

The immediate return without error can cause a system hang. For example,
vwaitforio() could end up spinning if called during execve(2) because
the thread did not enter sleep and other threads were not able to finish
the I/O.

tsleep
vwaitforio
nfs_flush
nfs_close
VOP_CLOSE
vn_closefile
fdrop
closef
fdcloseexec
sys_execve

Fix the issue by checking (p->p_flag & P_SUSPSINGLE) instead of
(p->p_p->ps_single != NULL) in sleep_setup_signal(). The former is more
selective than the latter and allows the thread that invokes execve(2)
enter sleep normally.

Bug report, change bisecting and testing help by Pavel Korovin

OK claudio@ mpi@

1 files changed, 2 insertions, 2 deletions

diff --git a/sys/kern/kern_synch.c b/sys/kern/kern_synch.c
index efb012278b1..bb77ee31048 100644
--- a/sys/kern/kern_synch.c
+++ b/sys/kern/kern_synch.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_synch.c,v 1.166 2020/03/20 17:13:51 cheloha Exp $	*/
+/*	$OpenBSD: kern_synch.c,v 1.167 2020/03/23 15:42:10 visa Exp $	*/
 /*	$NetBSD: kern_synch.c,v 1.37 1996/04/22 01:38:37 christos Exp $	*/
 
 /*
@@ -480,7 +480,7 @@ sleep_setup_signal(struct sleep_state *sls)
 	 * stopped, p->p_wchan will be 0 upon return from CURSIG.
 	 */
 	atomic_setbits_int(&p->p_flag, P_SINTR);
-	if (p->p_p->ps_single != NULL || (sls->sls_sig = CURSIG(p)) != 0) {
+	if ((p->p_flag & P_SUSPSINGLE) || (sls->sls_sig = CURSIG(p)) != 0) {
 		unsleep(p);
 		p->p_stat = SONPROC;
 		sls->sls_do_sleep = 0;