Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers

[Jilles Tjoelker <jilles@stack.nl>]

On Sun, Dec 11, 2016 at 07:54:51PM +0200, Konstantin Belousov wrote:
> On Sun, Dec 11, 2016 at 01:46:38PM +0100, Jilles Tjoelker wrote:
> > As reported in https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=213928
> > reapers do not receive SIGCHLD when inheriting zombies, although they do
> > receive SIGCHLD when an inherited descendant process later terminates
> > and are awakened when in a wait call for a matching process. This should
> > probably be fixed.
> I agree, in principle.  Could you update your tests/sys/kern/reaper.c to
> include this scenario ?

I tested with the patch below. The new test case
reaper_sigchld_child_first already passes and I have marked
reaper_sigchld_grandchild_first as an expected timeout.

> Untested change to the kernel side is below.

> diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
> index f4f453c3556..92899740eef 100644
> --- a/sys/kern/kern_exit.c
> +++ b/sys/kern/kern_exit.c
> @@ -455,6 +455,12 @@ exit1(struct thread *td, int rval, int signo)
>  
>  		if (!(q->p_flag & P_TRACED)) {
>  			proc_reparent(q, q->p_reaper);
> +			if (q->p_state == PRS_ZOMBIE) {
> +				PROC_LOCK(q->p_reaper);
> +				pksignal(q->p_reaper, SIGCHLD, q->p_ksi);
> +				wakeup(q->p_reaper);
> +				PROC_UNLOCK(q->p_reaper);
> +			}
>  		} else {
>  			/*
>  			 * Traced processes are killed since their existence

This change makes reaper_sigchld_grandchild_first pass.

The wakeup added here is redundant with the one a few lines above:
        if (q != NULL)          /* only need this if any child is S_ZOMB */
                wakeup(q->p_reaper);

This is also clear because reaper_wait_grandchild_first already passes.

Index: tests/sys/kern/reaper.c
===================================================================
--- tests/sys/kern/reaper.c	(revision 309839)
+++ tests/sys/kern/reaper.c	(working copy)
@@ -35,6 +35,11 @@
 #include <signal.h>
 #include <unistd.h>
 
+static void
+dummy_sighandler(int sig __unused, siginfo_t *info __unused, void *ctx __unused)
+{
+}
+
 ATF_TC_WITHOUT_HEAD(reaper_wait_child_first);
 ATF_TC_BODY(reaper_wait_child_first, tc)
 {
@@ -129,6 +134,163 @@
 	ATF_CHECK_EQ(2, r);
 }
 
+ATF_TC(reaper_sigchld_child_first);
+ATF_TC_HEAD(reaper_sigchld_child_first, tc)
+{
+	atf_tc_set_md_var(tc, "timeout", "2");
+}
+ATF_TC_BODY(reaper_sigchld_child_first, tc)
+{
+	struct sigaction act;
+	sigset_t mask;
+	siginfo_t info;
+	pid_t parent, child, grandchild, pid;
+	int r;
+	int pip[2];
+
+	/* Be paranoid. */
+	pid = waitpid(-1, NULL, WNOHANG);
+	ATF_REQUIRE(pid == -1 && errno == ECHILD);
+
+	act.sa_sigaction = dummy_sighandler;
+	act.sa_flags = SA_SIGINFO | SA_RESTART;
+	r = sigemptyset(&act.sa_mask);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigaction(SIGCHLD, &act, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	r = sigemptyset(&mask);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigaddset(&mask, SIGCHLD);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigprocmask(SIG_BLOCK, &mask, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	parent = getpid();
+	r = procctl(P_PID, parent, PROC_REAP_ACQUIRE, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	r = pipe(pip);
+	ATF_REQUIRE_EQ(0, r);
+
+	child = fork();
+	ATF_REQUIRE(child != -1);
+	if (child == 0) {
+		if (close(pip[1]) != 0)
+			_exit(100);
+		grandchild = fork();
+		if (grandchild == -1)
+			_exit(101);
+		else if (grandchild == 0) {
+			if (read(pip[0], &(uint8_t){ 0 }, 1) != 0)
+				_exit(102);
+			if (getppid() != parent)
+				_exit(103);
+			_exit(2);
+		} else
+			_exit(3);
+	}
+
+	r = sigwaitinfo(&mask, &info);
+	ATF_REQUIRE_EQ(SIGCHLD, r);
+	ATF_CHECK_EQ(SIGCHLD, info.si_signo);
+	ATF_CHECK_EQ(CLD_EXITED, info.si_code);
+	ATF_CHECK_EQ(3, info.si_status);
+	ATF_CHECK_EQ(child, info.si_pid);
+
+	pid = waitpid(child, NULL, 0);
+	ATF_REQUIRE_EQ(child, pid);
+
+	r = close(pip[1]);
+	ATF_REQUIRE_EQ(0, r);
+
+	r = sigwaitinfo(&mask, &info);
+	ATF_REQUIRE_EQ(SIGCHLD, r);
+	ATF_CHECK_EQ(SIGCHLD, info.si_signo);
+	ATF_CHECK_EQ(CLD_EXITED, info.si_code);
+	ATF_CHECK_EQ(2, info.si_status);
+	grandchild = info.si_pid;
+	ATF_REQUIRE(grandchild > 0);
+	ATF_REQUIRE(grandchild != parent);
+	ATF_REQUIRE(grandchild != child);
+
+	pid = waitpid(-1, NULL, 0);
+	ATF_REQUIRE_EQ(grandchild, pid);
+
+	r = close(pip[0]);
+	ATF_REQUIRE_EQ(0, r);
+}
+
+ATF_TC(reaper_sigchld_grandchild_first);
+ATF_TC_HEAD(reaper_sigchld_grandchild_first, tc)
+{
+	atf_tc_set_md_var(tc, "timeout", "2");
+}
+ATF_TC_BODY(reaper_sigchld_grandchild_first, tc)
+{
+	struct sigaction act;
+	sigset_t mask;
+	siginfo_t info;
+	pid_t parent, child, grandchild, pid;
+	int r;
+
+	atf_tc_expect_timeout("bug 213928");
+
+	/* Be paranoid. */
+	pid = waitpid(-1, NULL, WNOHANG);
+	ATF_REQUIRE(pid == -1 && errno == ECHILD);
+
+	act.sa_sigaction = dummy_sighandler;
+	act.sa_flags = SA_SIGINFO | SA_RESTART;
+	r = sigemptyset(&act.sa_mask);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigaction(SIGCHLD, &act, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	r = sigemptyset(&mask);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigaddset(&mask, SIGCHLD);
+	ATF_REQUIRE_EQ(0, r);
+	r = sigprocmask(SIG_BLOCK, &mask, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	parent = getpid();
+	r = procctl(P_PID, parent, PROC_REAP_ACQUIRE, NULL);
+	ATF_REQUIRE_EQ(0, r);
+
+	child = fork();
+	ATF_REQUIRE(child != -1);
+	if (child == 0) {
+		grandchild = fork();
+		if (grandchild == -1)
+			_exit(101);
+		else if (grandchild == 0)
+			_exit(2);
+		else {
+			if (waitid(P_PID, grandchild, NULL,
+			    WNOWAIT | WEXITED) != 0)
+				_exit(102);
+			_exit(3);
+		}
+	}
+
+	pid = waitpid(child, NULL, 0);
+	ATF_REQUIRE_EQ(child, pid);
+
+	r = sigwaitinfo(&mask, &info);
+	ATF_REQUIRE_EQ(SIGCHLD, r);
+	ATF_CHECK_EQ(SIGCHLD, info.si_signo);
+	ATF_CHECK_EQ(CLD_EXITED, info.si_code);
+	ATF_CHECK_EQ(2, info.si_status);
+	grandchild = info.si_pid;
+	ATF_REQUIRE(grandchild > 0);
+	ATF_REQUIRE(grandchild != parent);
+	ATF_REQUIRE(grandchild != child);
+
+	pid = waitpid(-1, NULL, 0);
+	ATF_REQUIRE_EQ(grandchild, pid);
+}
+
 ATF_TC_WITHOUT_HEAD(reaper_status);
 ATF_TC_BODY(reaper_status, tc)
 {
@@ -484,6 +646,8 @@
 
 	ATF_TP_ADD_TC(tp, reaper_wait_child_first);
 	ATF_TP_ADD_TC(tp, reaper_wait_grandchild_first);
+	ATF_TP_ADD_TC(tp, reaper_sigchld_child_first);
+	ATF_TP_ADD_TC(tp, reaper_sigchld_grandchild_first);
 	ATF_TP_ADD_TC(tp, reaper_status);
 	ATF_TP_ADD_TC(tp, reaper_getpids);
 	ATF_TP_ADD_TC(tp, reaper_kill_badsig);

-- 
Jilles Tjoelker
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