[src/trunk]: src/sys/kern ttygetinfo(): avoid crash with zombies. From skrll@...

[ad <ad%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/78cccc6b0fc0
branches:  trunk
changeset: 466913:78cccc6b0fc0
user:      ad <ad%NetBSD.org@localhost>
date:      Mon Jan 06 11:18:51 2020 +0000

description:
ttygetinfo(): avoid crash with zombies. From skrll@, tweaked by me.

diffstat:

 sys/kern/tty.c |  40 +++++++++++++++++++++++++++-------------
 1 files changed, 27 insertions(+), 13 deletions(-)

diffs (87 lines):

diff -r 6f784cc35349 -r 78cccc6b0fc0 sys/kern/tty.c
--- a/sys/kern/tty.c    Mon Jan 06 11:16:35 2020 +0000
+++ b/sys/kern/tty.c    Mon Jan 06 11:18:51 2020 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: tty.c,v 1.283 2020/01/02 16:52:55 skrll Exp $  */
+/*     $NetBSD: tty.c,v 1.284 2020/01/06 11:18:51 ad Exp $     */
 
 /*-
  * Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -63,7 +63,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.283 2020/01/02 16:52:55 skrll Exp $");
+__KERNEL_RCSID(0, "$NetBSD: tty.c,v 1.284 2020/01/06 11:18:51 ad Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_compat_netbsd.h"
@@ -2533,11 +2533,13 @@
        const char      *msg;
        char            lmsg[100];
        long            rss;
+       bool            again = false;
 
        KASSERT(mutex_owned(proc_lock));
 
        *buf = '\0';
 
+ retry:
        if (tp->t_session == NULL)
                msg = "not a controlling terminal\n";
        else if (tp->t_pgrp == NULL)
@@ -2568,11 +2570,26 @@
                        if (p->p_lock != oldpick->p_lock)
                                mutex_exit(oldpick->p_lock);
                }
-               if (fromsig &&
-                   (SIGACTION_PS(pick->p_sigacts, SIGINFO).sa_flags &
-                   SA_NOKERNINFO))
-                       return;
-               msg = NULL;
+
+               if (pick != NULL) {
+                       mutex_enter(pick->p_lock);
+                       if (P_ZOMBIE(pick)) {
+                               mutex_exit(pick->p_lock);
+                               pick = NULL;
+                               if (!again) {
+                                       again = true;
+                                       goto retry;
+                               }
+                               msg = "found only zombie processes\n";
+                       }
+                       if (fromsig &&
+                           (SIGACTION_PS(pick->p_sigacts, SIGINFO).sa_flags &
+                           SA_NOKERNINFO)) {
+                               mutex_exit(pick->p_lock);
+                               return;
+                       }
+                       msg = NULL;
+               }
        }
 
        /* Print load average. */
@@ -2589,7 +2606,7 @@
            pick->p_pid);
        strlcat(buf, lmsg, bufsz);
 
-       mutex_enter(pick->p_lock);
+       KASSERT(mutex_owned(pick->p_lock));
        LIST_FOREACH(l, &pick->p_lwps, l_sibling) {
                const char *lp;
                lwp_lock(l);
@@ -2679,11 +2696,8 @@
        KASSERT(mutex_owned(p1->p_lock));
        KASSERT(mutex_owned(p2->p_lock));
 
-       if ((l1 = LIST_FIRST(&p1->p_lwps)) == NULL)
-               return 1;
-
-       if ((l2 = LIST_FIRST(&p2->p_lwps)) == NULL)
-               return 0;
+       l1 = LIST_FIRST(&p1->p_lwps);
+       l2 = LIST_FIRST(&p2->p_lwps);
 
        return proc_compare(p1, l1, p2, l2);
 }