bin/108390: [libc] [patch] wait4() erroneously waits for all children when SIGCHLD is SIG_IGN [regression]

[Kostik Belousov]

Further check on Solaris revealed that for the case where SIGCHLD is
ignored, wait4() returned -1/ECHLD, conforming to the FreeBSD behaviour
of reparenting to init.

Unless further comments are given, I will commit this in several days:

diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 4255734..c35c6f2 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -504,13 +504,13 @@ exit1(struct thread *td, int rv)
 		proc_reparent(p, initproc);
 		p->p_sigparent = SIGCHLD;
 		PROC_LOCK(p->p_pptr);
+
 		/*
-		 * If this was the last child of our parent, notify
-		 * parent, so in case he was wait(2)ing, he will
+		 * Notify parent, so in case he was wait(2)ing or
+		 * executiing waitpid(2) with our pid, he will
 		 * continue.
 		 */
-		if (LIST_EMPTY(&pp->p_children))
-			wakeup(pp);
+		wakeup(pp);
 	} else
 		mtx_unlock(&p->p_pptr->p_sigacts->ps_mtx);
 
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