svn commit: r205806 - stable/8/etc

Doug Barton dougb at FreeBSD.org
Mon Apr 5 03:56:31 UTC 2010


On 03/29/10 10:32, Jilles Tjoelker wrote:
> On Sun, Mar 28, 2010 at 04:10:38PM -0700, Doug Barton wrote:
>> On 03/28/10 14:06, Jilles Tjoelker wrote:
>>> On Sun, Mar 28, 2010 at 01:28:42PM -0700, Doug Barton wrote:
>>>> Probably my fault for not saying something sooner, but there is a
>>>> problem with the code in head that sometimes causes it to loop
>>>> repeatedly even though pwait exits successfully. I am trying to track it
>>>> down, but since it only happens about once every 10 shutdowns it's been
>>>> difficult.
> 
>>> There is a difference between the two methods in what is waited for
>>> exactly. pwait(1) will wait for the process to terminate; if it is
>>> applied to a zombie it will return immediately (printing the exit status
>>> if -v was given). On the other hand, kill(1) will continue to return
>>> success until the process has been waited for by its parent.
> 
>> The process that I see this with most often is devd, does that fit the
>> model you're describing?
> 
> Possibly. This would mainly happen because init has been busy, I think
> (or if the parent isn't init).
> 
>> What are the implications of moving on after a
>> successful pwait even though there is still a zombie process?
> 
> For shutdown/stop, nothing.
> 
> For restart, there may be problems if a restarted daemon checks the
> validity of the pid in the pidfile using kill().

Ok, in that case I'm not really comfortable with the idea of ignoring
the results of kill -0, however I've come up with what I think is a good
solution in the attached patch. Based on your description and my ongoing
analysis the problem I was seeing with the long string of the same pid
repeated over and over seems to be a side effect of pwait returning
successfully (thus the || sleep 2 never kicks in) but 'kill -0' still
being able to see the pid. So, I've moved the sleep up so that if we're
not in the first pass but kill -0 is still seeing the pid that we sleep
for 1 second, then proceed. I think that'll handle both the problem I
saw, and the odd case where pwait doesn't return successfully.

Sound good?


Doug

-- 

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-------------- next part --------------
Index: rc.subr
===================================================================
--- rc.subr	(revision 206117)
+++ rc.subr	(working copy)
@@ -359,12 +359,14 @@
 	if [ -z "$_list" ]; then
 		return
 	fi
-	_prefix=
+
+	local _prefix=
 	while true; do
 		_nlist="";
 		for _j in $_list; do
 			if kill -0 $_j 2>/dev/null; then
 				_nlist="${_nlist}${_nlist:+ }$_j"
+				[ -n "$_prefix" ] && sleep 1
 			fi
 		done
 		if [ -z "$_nlist" ]; then
@@ -373,7 +375,7 @@
 		_list=$_nlist
 		echo -n ${_prefix:-"Waiting for PIDS: "}$_list
 		_prefix=", "
-		pwait $_list 2>/dev/null || sleep 2
+		pwait $_list 2>/dev/null
 	done
 	if [ -n "$_prefix" ]; then
 		echo "."


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