[libvirt PATCH 1/5] nwfilter: stop using recursive mutex for IP learning

[Laine Stump]

On 2/25/22 10:30 AM, Daniel P. Berrangé wrote:
> The virNWFilterLockIface method is only called from one place,
> the learnIPAddressThread method.

nwfilter_gentech_driver.c:virNWFilterDoInstantiate() and 
_virNWFilterTeardownFilter() also call virNWFilterLockIface.

And there is this call chain from learnIPAddressThread() that ends up at 
one or the other of those:

learnIPAddressThread()
   virNWFilterInstantiateFilterLate()
     virNWFilterInstantiateFilterUpdate()
       virNWFilterDoInstantiate() <----
     _virNWFilterTeardownFilter() <----

But of course just prior to calling virNWFilterINstantiateFilterLate(), 
learnIPAddressThread() calls:

   virNWFilterUnlockIface(req->binding->portdevname);

which matches the previous virNWFilterLockIface(), so there shouldn't be 
a problem for the learnIPAddressThread at least.

I'm not sure about the threads of other calls to 
virNWFilterDoInstantiate/TeardownFilter though, haven't tried to 
decipher them yet.

> This is the entry point for
> the learning thread on the interface in question. As such
> there is never any recursive locking on this mutex from the
> same thread. This appears to have been the case since the
> code was first introduced. Thus a plain mutex is sufficient.
> 
> Signed-off-by: Daniel P. Berrangé <berrange at redhat.com>
> ---
>   src/nwfilter/nwfilter_learnipaddr.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/nwfilter/nwfilter_learnipaddr.c b/src/nwfilter/nwfilter_learnipaddr.c
> index fb552bd1e6..4840b0539f 100644
> --- a/src/nwfilter/nwfilter_learnipaddr.c
> +++ b/src/nwfilter/nwfilter_learnipaddr.c
> @@ -151,7 +151,7 @@ virNWFilterLockIface(const char *ifname)
>       if (!ifaceLock) {
>           ifaceLock = g_new0(virNWFilterIfaceLock, 1);
>   
> -        if (virMutexInitRecursive(&ifaceLock->lock) < 0) {
> +        if (virMutexInit(&ifaceLock->lock) < 0) {
>               virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
>                              _("mutex initialization failed"));
>               g_free(ifaceLock);