[OSSTEST PATCH] TestSupport: use timeout(1)

[OSSTEST PATCH] TestSupport: use timeout(1)

[Ian Jackson]

If a command we run times out, the machinery in tcmdex() will arrange
for the ts-* script to spot the timeout, and stop waiting for it.

However it is also necessary for the command we ran to die.  It has a
copy of the owner daemon fd, so if it doesn't, our resources won't get
freed.  In sufficiently exciting bugs, our allocation might continue
indefinitely, while a subprocess of ours hangs on after we are long
gone.

timeout(1) does not print a message when the process times out (!)  So
we can't do away with the logic in tcmdex().  We set the timeout(1)
timeout to 30s more than our own timeout, so that tcmdex() will time
out first and print a message.

We could use alarm(1) as we do in Osstest/Serial/sympathy.pm but that
program isn't packaged and its unsophisticated approach is not really
appropriate for arbitrary nonconsenting programs.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>
---
 Osstest/TestSupport.pm |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/Osstest/TestSupport.pm b/Osstest/TestSupport.pm
index a3b6936..ca680c0 100644
--- a/Osstest/TestSupport.pm
+++ b/Osstest/TestSupport.pm
@@ -388,7 +388,10 @@ sub sshopts () {
 sub tcmdex {
     my ($timeout,$stdout,$cmd,$optsref,@args) = @_;
     logm("executing $cmd ... @args");
-    my $r= cmd($timeout,$stdout, $cmd,@$optsref,@args);
+    # We use timeout(1) as a backstop, in case $cmd doesn't die.  We
+    # need $cmd to die because we won't release the resources we own
+    # until all of our children are dead.
+    my $r= cmd($timeout,$stdout, 'timeout',$timeout+30, $cmd,@$optsref,@args);
     $r and die "status $r";
 }
 
-- 
1.7.10.4

Re: [OSSTEST PATCH] TestSupport: use timeout(1)

[Ian Campbell]

On Mon, 2014-12-08 at 14:08 +0000, Ian Jackson wrote:
> If a command we run times out, the machinery in tcmdex() will arrange
> for the ts-* script to spot the timeout, and stop waiting for it.
> 
> However it is also necessary for the command we ran to die.  It has a
> copy of the owner daemon fd, so if it doesn't, our resources won't get
> freed.  In sufficiently exciting bugs, our allocation might continue
> indefinitely, while a subprocess of ours hangs on after we are long
> gone.
> 
> timeout(1) does not print a message when the process times out (!)  So
> we can't do away with the logic in tcmdex().

I think you mean s/tcmdex/cmd/ in a few places here, since cmd() is
where all the existing timeout stuff is.

>   We set the timeout(1)
> timeout to 30s more than our own timeout, so that tcmdex() will time
> out first and print a message.
> 
> We could use alarm(1) as we do in Osstest/Serial/sympathy.pm but that
> program isn't packaged and its unsophisticated approach is not really
> appropriate for arbitrary nonconsenting programs.
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

Apart from that niggle:
Acked-by: Ian Campbell <ian.campbell@citrix.com>


> ---
>  Osstest/TestSupport.pm |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/Osstest/TestSupport.pm b/Osstest/TestSupport.pm
> index a3b6936..ca680c0 100644
> --- a/Osstest/TestSupport.pm
> +++ b/Osstest/TestSupport.pm
> @@ -388,7 +388,10 @@ sub sshopts () {
>  sub tcmdex {
>      my ($timeout,$stdout,$cmd,$optsref,@args) = @_;
>      logm("executing $cmd ... @args");
> -    my $r= cmd($timeout,$stdout, $cmd,@$optsref,@args);
> +    # We use timeout(1) as a backstop, in case $cmd doesn't die.  We
> +    # need $cmd to die because we won't release the resources we own
> +    # until all of our children are dead.
> +    my $r= cmd($timeout,$stdout, 'timeout',$timeout+30, $cmd,@$optsref,@args);
>      $r and die "status $r";
>  }
>