[libvirt] [PATCH] Firewall : let libvirtd proceed after verifying locking args

[Prerna Saxena]

Ping !
On Friday 26 December 2014 03:54 PM, Prerna Saxena wrote:
> I recently encountered a situation where an unclean ebtables shutdown
> caused /var/lib/ebtables/lock to be left behind. When libvirtd was
> started on such a system, it caused libvirtd to "hang". Reason:
> While probing to check if locking was supported, libvirt runs this
> command synchronously :
>   #  /usr/sbin/ebtables --concurrent -L
> And this seemed to go on with msgs like :
>  Trying to obtain lock /var/lib/ebtables/lock
>  Trying to obtain lock /var/lib/ebtables/lock
>  Trying to obtain lock /var/lib/ebtables/lock
>
> Result:
> Libvirtd never recovered from this scenario, and the system was
> essentially unable to start any VMs.
>
> The following patch fixes this scenario:
> -----------------------------------------------------------
> >From ec245eccc03e8a69dc2c2e6edbf30a7b34eb74d0 Mon Sep 17 00:00:00 2001
> From: Prerna Saxena <prerna at linux.vnet.ibm.com>
> Date: Fri, 26 Dec 2014 15:24:45 -0500
> Subject: [PATCH] Firewall : let libvirtd proceed after verifying valid locking
>  args.
>
> Commit dc33e6e4a5a5d42 introduces locking args to be run with [eb/ip]tables to
> determine whether locking is supported. However, this command needs to be
> run asynchronously ( as against its present synchronous run), and needs to be
> gracefully terminated once the job is done. Else it can potentially stall libvirtd
> with messages like :
>  "Trying to acquire lock ..."
>
> Signed-off-by: Prerna Saxena <prerna at linux.vnet.ibm.com>
> ---
>  src/util/virfirewall.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/src/util/virfirewall.c b/src/util/virfirewall.c
> index b536912..c120717 100644
> --- a/src/util/virfirewall.c
> +++ b/src/util/virfirewall.c
> @@ -121,12 +121,16 @@ virFirewallCheckUpdateLock(bool *lockflag,
>  {
>      int status; /* Ignore failed commands without logging them */
>      virCommandPtr cmd = virCommandNewArgs(args);
> -    if (virCommandRun(cmd, &status) < 0 || status) {
> +    status = virCommandRunAsync(cmd, NULL);
> +    if (status < 0) {
>          VIR_INFO("locking not supported by %s", args[0]);
> +        goto cleanup;
>      } else {
>          VIR_INFO("using locking for %s", args[0]);
>          *lockflag = true;
>      }
> +cleanup:
> +    virCommandAbort(cmd);
>      virCommandFree(cmd);
>  }
>

-- 
Prerna Saxena

Linux Technology Centre,
IBM Systems and Technology Lab,
Bangalore, India