* NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
[not found] ` <20161208132842.5d7940bd@eto-mona.office.smartweb.sk>
@ 2016-12-08 20:23 ` Jonathan de Boyne Pollard
2016-12-11 12:46 ` Jilles Tjoelker
0 siblings, 1 reply; 6+ messages in thread
From: Jonathan de Boyne Pollard @ 2016-12-08 20:23 UTC (permalink / raw)
To: FreeBSD Hackers, supervision
Martin "eto" Misuth:
> I think that might be the reason why my PID1 s6-svscan on FreeBSD is
> accumulating zombies sometimes (seems like it is affected by dead
> descendants of ssh and my experiments). [...]
> Anyway as you are probably much closer to FreeBSD team than I am, [...]
I'm not. You have the same access as I and the rest of the world have.
For what it's worth, I've seen similar behaviour with zombies lying
around. If we can nail it down you can file a kernel bug report.
Have you checked that you aren't getting a NOTE_EXIT?
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
2016-12-08 20:23 ` NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers Jonathan de Boyne Pollard
@ 2016-12-11 12:46 ` Jilles Tjoelker
2016-12-11 17:54 ` Konstantin Belousov
2016-12-13 12:39 ` Jonathan de Boyne Pollard
0 siblings, 2 replies; 6+ messages in thread
From: Jilles Tjoelker @ 2016-12-11 12:46 UTC (permalink / raw)
To: Jonathan de Boyne Pollard; +Cc: FreeBSD Hackers, supervision
On Thu, Dec 08, 2016 at 08:23:29PM +0000, Jonathan de Boyne Pollard wrote:
> Martin "eto" Misuth:
> > I think that might be the reason why my PID1 s6-svscan on FreeBSD is
> > accumulating zombies sometimes (seems like it is affected by dead
> > descendants of ssh and my experiments). [...]
> > Anyway as you are probably much closer to FreeBSD team than I am, [...]
> I'm not. You have the same access as I and the rest of the world have.
> For what it's worth, I've seen similar behaviour with zombies lying
> around. If we can nail it down you can file a kernel bug report.
> Have you checked that you aren't getting a NOTE_EXIT?
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.
NOTE_TRACK has the inherent problem of what to do when NOTE_TRACKERR
happens and has problems with process ID reuse, so it seems better to
use reaper instead of it.
--
Jilles Tjoelker
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
2016-12-11 12:46 ` Jilles Tjoelker
@ 2016-12-11 17:54 ` Konstantin Belousov
2016-12-11 22:23 ` Jilles Tjoelker
2016-12-13 12:39 ` Jonathan de Boyne Pollard
1 sibling, 1 reply; 6+ messages in thread
From: Konstantin Belousov @ 2016-12-11 17:54 UTC (permalink / raw)
To: Jilles Tjoelker; +Cc: FreeBSD Hackers, Jonathan de Boyne Pollard, supervision
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 ?
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
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
2016-12-11 17:54 ` Konstantin Belousov
@ 2016-12-11 22:23 ` Jilles Tjoelker
2016-12-12 11:12 ` Konstantin Belousov
0 siblings, 1 reply; 6+ messages in thread
From: Jilles Tjoelker @ 2016-12-11 22:23 UTC (permalink / raw)
To: Konstantin Belousov
Cc: FreeBSD Hackers, Jonathan de Boyne Pollard, supervision
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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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
2016-12-11 22:23 ` Jilles Tjoelker
@ 2016-12-12 11:12 ` Konstantin Belousov
0 siblings, 0 replies; 6+ messages in thread
From: Konstantin Belousov @ 2016-12-12 11:12 UTC (permalink / raw)
To: Jilles Tjoelker; +Cc: FreeBSD Hackers, Jonathan de Boyne Pollard, supervision
On Sun, Dec 11, 2016 at 11:23:28PM +0100, Jilles Tjoelker wrote:
> 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);
I removed additional wakeup, it should be innocent. Might be the better
change is to remove the lines you cited above and do wakeups inside the
loop after reparenting. But I kept it that way for now.
>
> This is also clear because reaper_wait_grandchild_first already passes.
>
> Index: tests/sys/kern/reaper.c
Thank you, I verified that all tests pass with the patched kernel and
removed timeouts from your reaper_sigchld_*child_first new tests.
The kernel chunk is committed as r309886, please commit tests.
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^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers
2016-12-11 12:46 ` Jilles Tjoelker
2016-12-11 17:54 ` Konstantin Belousov
@ 2016-12-13 12:39 ` Jonathan de Boyne Pollard
1 sibling, 0 replies; 6+ messages in thread
From: Jonathan de Boyne Pollard @ 2016-12-13 12:39 UTC (permalink / raw)
To: FreeBSD Hackers, supervision
Jilles Tjoelker:
> This should probably be fixed.
There's another more insidious bug hiding inside kevent() somewhere that
causes a kernel abend complaining about a sleeping thread holding a
non-sleepable lock. One needs to make fairly heavy use of kevent() in
order to trigger it, I believe, as I have only seen it so far on systems
that do.
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^ permalink raw reply [flat|nested] 6+ messages in thread
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2016-12-08 20:23 ` NOTE_TRACK, EVFILT_PROC, kqueue, and subreapers Jonathan de Boyne Pollard
2016-12-11 12:46 ` Jilles Tjoelker
2016-12-11 17:54 ` Konstantin Belousov
2016-12-11 22:23 ` Jilles Tjoelker
2016-12-12 11:12 ` Konstantin Belousov
2016-12-13 12:39 ` Jonathan de Boyne Pollard
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