From: anton <anton@openbsd.org>
Date: Fri, 29 Oct 2021 15:52:44 +0000 (+0000)
Subject: poll needs similar treatment as select recently gained in order to not
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=fdbd9592128c339e250bf4fe1f34ceadf7be2270;p=openbsd

poll needs similar treatment as select recently gained in order to not
mask failed kqueue_register() attempts which in turn causes the thread to
end up sleeping as opposed of propagating the failure to user space.

Regression introduced in the recent switch to implement poll on top of
kqueue.

Thanks to Larry Hynes <larry at larryhynes dot com> for reporting and
Leah Neukirchen <leah at vuxu dot org> for providing a reproducer; which
also already made its way into regress.

ok mpi@
---

diff --git a/sys/kern/sys_generic.c b/sys/kern/sys_generic.c
index cbe5d04c54f..9a10bcc0057 100644
--- a/sys/kern/sys_generic.c
+++ b/sys/kern/sys_generic.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sys_generic.c,v 1.138 2021/10/24 11:23:22 mpi Exp $	*/
+/*	$OpenBSD: sys_generic.c,v 1.139 2021/10/29 15:52:44 anton Exp $	*/
 /*	$NetBSD: sys_generic.c,v 1.24 1996/03/29 00:25:32 cgd Exp $	*/
 
 /*
@@ -1128,7 +1128,7 @@ doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
 {
 	struct kqueue_scan_state scan;
 	struct pollfd pfds[4], *pl = pfds;
-	int error, nevents = 0;
+	int error, ncollected, nevents = 0;
 	size_t sz;
 
 	/* Standards say no more than MAX_OPEN; this is possibly better. */
@@ -1154,14 +1154,14 @@ doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
 		dosigsuspend(p, *sigmask &~ sigcantmask);
 
 	/* Register kqueue events */
-	*retval = ppollregister(p, pl, nfds, &nevents);
+	ncollected = ppollregister(p, pl, nfds, &nevents);
 
 	/*
 	 * The poll/select family of syscalls has been designed to
 	 * block when file descriptors are not available, even if
 	 * there's nothing to wait for.
 	 */
-	if (nevents == 0) {
+	if (nevents == 0 && ncollected == 0) {
 		uint64_t nsecs = INFSLP;
 
 		if (timeout != NULL) {
@@ -1184,7 +1184,7 @@ doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
 		struct kevent kev[KQ_NEVENTS];
 		int i, ready, count;
 
-		/* Maxium number of events per iteration */
+		/* Maximum number of events per iteration */
 		count = MIN(nitems(kev), nevents);
 		ready = kqueue_scan(&scan, count, kev, timeout, p, &error);
 #ifdef KTRACE
@@ -1193,7 +1193,7 @@ doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
 #endif
 		/* Convert back events that are ready. */
 		for (i = 0; i < ready; i++)
-			*retval += ppollcollect(p, &kev[i], pl, nfds);
+			ncollected += ppollcollect(p, &kev[i], pl, nfds);
 
 		/*
 		 * Stop if there was an error or if we had enough
@@ -1205,6 +1205,7 @@ doppoll(struct proc *p, struct pollfd *fds, u_int nfds,
 		nevents -= ready;
 	}
 	kqueue_scan_finish(&scan);
+	*retval = ncollected;
 done:
 	/*
 	 * NOTE: poll(2) is not restarted after a signal and EWOULDBLOCK is