Re: [PATCH v2 1/4] SUNRPC: release per-net clients lock before callingPipeFS dentries creation

[Stanislav Kinsbursky]

27.02.2012 20:21, Myklebust, Trond ÐÐÑÐÑ:
> On Mon, 2012-02-27 at 19:50 +0400, Stanislav Kinsbursky wrote:
> > Lockdep is sad otherwise, because inode mutex is taken on PipeFS dentry
> > creation, which can be called on mount notification, where this per-net client
> > lock is taken on clients list walk.
> >
> > Signed-off-by: Stanislav Kinsbursky<skinsbursky@xxxxxxxxxxxxx>
> >
> > ---
> >   net/sunrpc/clnt.c |   10 +++++++---
> >   1 files changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/sunrpc/clnt.c b/net/sunrpc/clnt.c
> > index bb7ed2f3..ddb5741 100644
> > --- a/net/sunrpc/clnt.c
> > +++ b/net/sunrpc/clnt.c
> > @@ -84,7 +84,7 @@ static void rpc_register_client(struct rpc_clnt *clnt)
> >   	struct sunrpc_net *sn = net_generic(clnt->cl_xprt->xprt_net, sunrpc_net_id);
> >
> >   	spin_lock(&sn->rpc_client_lock);
> > -	list_add(&clnt->cl_clients,&sn->all_clients);
> > +	list_add_tail(&clnt->cl_clients,&sn->all_clients);
> >   	spin_unlock(&sn->rpc_client_lock);
> >   }
> >
> > @@ -208,15 +208,19 @@ static int rpc_pipefs_event(struct notifier_block *nb, unsigned long event,
> >   			    void *ptr)
> >   {
> >   	struct super_block *sb = ptr;
> > -	struct rpc_clnt *clnt;
> > +	struct rpc_clnt *clnt, *tmp;
> >   	int error = 0;
> >   	struct sunrpc_net *sn = net_generic(sb->s_fs_info, sunrpc_net_id);
> >
> >   	spin_lock(&sn->rpc_client_lock);
> > -	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
> > +	list_for_each_entry_safe(clnt, tmp,&sn->all_clients, cl_clients) {
> > +		atomic_inc(&clnt->cl_count);
> > +		spin_unlock(&sn->rpc_client_lock);
> >   		error = __rpc_pipefs_event(clnt, event, sb);
> > +		rpc_release_client(clnt);
> >   		if (error)
> >   			break;
> > +		spin_lock(&sn->rpc_client_lock);
> >   	}
> >   	spin_unlock(&sn->rpc_client_lock);
> >   	return error;
>
> This won't be safe. Nothing guarantees that 'tmp' remains valid after
> you drop the spin_lock.
>
> I think you rather need to add a check for whether clnt->cl_dentry is in
> the right state (NULL if RPC_PIPEFS_UMOUNT or non-NULL if
> RPC_PIPEFS_MOUNT) before deciding whether or not to atomic_inc() and
> drop the lock, so that you can restart the loop after calling
> __rpc_pipefs_event().

Gmmm.
Please, correct me, if I'm wrong, that you are proposing something like this:

  	spin_lock(&sn->rpc_client_lock);
again:
	list_for_each_entry(clnt,&sn->all_clients, cl_clients) {
		if ((event == RPC_PIPEFS_MOUNT) && clnt->cl_dentry) ||
		    (event == RPC_PIPEFS_UMOUNT) && !clnt->cl_dentry))
			continue;
		atomic_inc(&clnt->cl_count);
		spin_unlock(&sn->rpc_client_lock);
   		error = __rpc_pipefs_event(clnt, event, sb);
		rpc_release_client(clnt);
		spin_lock(&sn->rpc_client_lock);
   		if (error)
   			break;
		goto again;
   	}
   	spin_unlock(&sn->rpc_client_lock);


--
Best regards,
Stanislav Kinsbursky
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