Re: git: kernel: Remove an extra p_lock == 0 check
:commit 4a7e6f5530dd5eb9ca5195aeb18a0ebd59b0fa41
:Author: YONETANI Tomokazu <y0netan1@dragonflybsd.org>
:Date: Thu Jun 2 14:17:46 2011 +0900
:
: kernel: Remove an extra p_lock == 0 check
:
: proc_remove_zombie() waits for p_lock to drop to zero before removing
: the process off zombproc, so this assertion is not needed (any more).
:
:Summary of changes:
: sys/kern/kern_exit.c | 1 -
: 1 files changed, 0 insertions(+), 1 deletions(-)
:
:http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff/4a7e6f5530dd5eb9ca5195aeb18a0ebd59b0fa41
:
I think we need one more addition. Since p_lock can be acquired during
the process removal there need to be a final wait loop after the proc
has been removed from all queues, just before the kfree(p). It will be
a very rare case but it definitely can still occur if e.g. the SYSCTL_OUT
code blocks on a VM fault or something like that.
(untested patch below)
-Matt
Matthew Dillon
<dillon@backplane.com>
diff --git a/sys/kern/kern_exit.c b/sys/kern/kern_exit.c
index 1e5a110..274f153 100644
--- a/sys/kern/kern_exit.c
+++ b/sys/kern/kern_exit.c
@@ -934,6 +934,17 @@ loop:
}
vm_waitproc(p);
+
+ /*
+ * Temporary refs may still have been acquired while
+ * we removed the process, make sure they are all
+ * gone before kfree()ing. Now that the process has
+ * been removed from all lists and all references to
+ * it have gone away, no new refs can occur.
+ */
+ while (p->p_lock)
+ tsleep(p, 0, "reap4", hz);
+
kfree(p, M_PROC);
nprocs--;
error = 0;
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