[src/trunk]: src/sys/dev/filemon When following process parent pointers, lock...

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

details:   https://anonhg.NetBSD.org/src/rev/1c305726fb7b
branches:  trunk
changeset: 342796:1c305726fb7b
user:      pgoyette <pgoyette%NetBSD.org@localhost>
date:      Sat Jan 09 07:27:31 2016 +0000

description:
When following process parent pointers, lock the new (parent) before
releasing the initial process.

diffstat:

 sys/dev/filemon/filemon.c |  19 ++++++++++++-------
 1 files changed, 12 insertions(+), 7 deletions(-)

diffs (49 lines):

diff -r be6a8c93bfb4 -r 1c305726fb7b sys/dev/filemon/filemon.c
--- a/sys/dev/filemon/filemon.c Sat Jan 09 03:33:53 2016 +0000
+++ b/sys/dev/filemon/filemon.c Sat Jan 09 07:27:31 2016 +0000
@@ -1,4 +1,4 @@
-/*      $NetBSD: filemon.c,v 1.26 2016/01/08 08:57:14 pgoyette Exp $ */
+/*      $NetBSD: filemon.c,v 1.27 2016/01/09 07:27:31 pgoyette Exp $ */
 /*
  * Copyright (c) 2010, Juniper Networks, Inc.
  *
@@ -25,7 +25,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: filemon.c,v 1.26 2016/01/08 08:57:14 pgoyette Exp $");
+__KERNEL_RCSID(0, "$NetBSD: filemon.c,v 1.27 2016/01/09 07:27:31 pgoyette Exp $");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
@@ -154,13 +154,14 @@
        struct filemon *filemon;
        struct proc * lp;
 
+       KASSERT(p != NULL);
        if (!TAILQ_EMPTY(&filemons_inuse)) {
+               /*
+                * make sure p cannot exit
+                * until we have moved on to p_pptr
+                */
+               rw_enter(&p->p_reflock, RW_READER);
                while (p) {
-                       /*
-                        * make sure p cannot exit
-                        * until we have moved on to p_pptr
-                        */
-                       rw_enter(&p->p_reflock, RW_READER);
                        TAILQ_FOREACH(filemon, &filemons_inuse, fm_link) {
                                if (p->p_pid == filemon->fm_pid) {
                                        rw_exit(&p->p_reflock);
@@ -169,6 +170,10 @@
                        }
                        lp = p;
                        p = p->p_pptr;
+
+                       /* lock parent before releasing child */
+                       if (p != NULL)
+                               rw_enter(&p->p_reflock, RW_READER);
                        rw_exit(&lp->p_reflock);
                }
        }