Hi
I have a report of a the BUG_ON in rpcb_getport_clnt being
triggered. This is:
/* Autobind on cloned rpc clients is discouraged */
BUG_ON(clnt->cl_parent != clnt);
It looks to me that while they might be discouraged, they are not
prevented and so having the BUG_ON is wrong.
When rpc_clone_client creates a clone, it sets cl_autobind to 0,
and gives the new client a reference to the same cl_xprt as the
original client.
The only effect of cl_autobind is to prevent rpc_force_rebind from
clearing the BOUND flag on ->cl_xprt.
So while a call to rpc_force_rebind on the clone will not clear that
flag, a call on the original client will clear that flag.
So a cloned client can still end up with a ->cl_xprt with the BOUND
flag clear.
So call_bind (which is present in the call trace under the oops) can
find that !xprt_bound, even when the client is a cloned client.
When this happens, ->rpcbind, which is rpcb_getport_clnt, goes BOOM.
What should happen when a clone client finds that its transport is no
longer bound? Should rpc_getport_async just do
clnt = task->tk_client->cl_parent;
??
Perplexed,
NeilBrown
On Tue, 2008-08-12 at 12:27 +1000, Neil Brown wrote:
> Hi
> I have a report of a the BUG_ON in rpcb_getport_clnt being
> triggered. This is:
> /* Autobind on cloned rpc clients is discouraged */
> BUG_ON(clnt->cl_parent != clnt);
>
> It looks to me that while they might be discouraged, they are not
> prevented and so having the BUG_ON is wrong.
>
> When rpc_clone_client creates a clone, it sets cl_autobind to 0,
> and gives the new client a reference to the same cl_xprt as the
> original client.
>
> The only effect of cl_autobind is to prevent rpc_force_rebind from
> clearing the BOUND flag on ->cl_xprt.
> So while a call to rpc_force_rebind on the clone will not clear that
> flag, a call on the original client will clear that flag.
>
> So a cloned client can still end up with a ->cl_xprt with the BOUND
> flag clear.
>
> So call_bind (which is present in the call trace under the oops) can
> find that !xprt_bound, even when the client is a cloned client.
>
> When this happens, ->rpcbind, which is rpcb_getport_clnt, goes BOOM.
>
> What should happen when a clone client finds that its transport is no
> longer bound? Should rpc_getport_async just do
> clnt = task->tk_client->cl_parent;
> ??
This shouldn't be a particularly urgent problem, since lockd should
normally be the only thing that needs to use the autobind functionality,
and it does not use cloned clients.
That said, I think that the answer is that cloned clients may indeed use
rpcbind as long as they share the same program number and version as the
parent.
IOW: we should probably rather BUG_ON() calls to rpc_bind_new_program()
if the parent has xprt->cl_autobind set.
Cheers
Trond