Re: [Libvir] [PATCH] avoid virsh hang due to missing virDomainFree(dom) call
"Daniel P. Berrange" <berrange(a)redhat.com> wrote:
On Wed, Jan 30, 2008 at 06:25:19PM +0100, Jim Meyering wrote:
> Without the following patch, this command would hang
>
> printf 'domuuid fc4\ndomstate fc4\n' \
> | ./virsh --connect test://$PWD/../docs/testnode.xml
>
> with this stack trace:
>
> __lll_lock_wait ...
> _L_lock_105 ...
> __pthread_mutex_lock ...
> virUnrefDomain (domain=0x6a8b30) at hash.c:884
> virDomainFree (domain=0x6a8b30) at libvirt.c:1211
> cmdDomstate (ctl=0x7fffea723390, cmd=0x6a8b10) at virsh.c:677
> vshCommandRun (ctl=0x7fffea723390, cmd=0x6a8b10) at virsh.c:4033
> main (argc=3, argv=0x7fffea7234e8) at virsh.c:501
>
> The problem is that cmdDomuuid didn't call virDomainFree(dom), so
> cmdDomstate hangs trying to do the Unref.
I don't understand why it would hang simply because it forgot to free
an object. Surely it ought to just be a memory leak not hang ? Each
individual libvirt API must always have a matched lock & unlock pair
in all codepaths, so a hang should only occur if an unlock is missing
in some codepath.
Well maybe virDomainFree is misnamed then.
It does more:
The missing virDomainFree calls cause that because
they are what is supposed to do the unlock.
virDomainFree calls virUnrefDomain, which calls virReleaseDomain
(when refs hits 0), which calls pthread_mutex_unlock.