Re: [PATCH] nfsd: unhash client before expiring it

["J. Bruce Fields" <bfields@fieldses.org>]

On Thu, Oct 10, 2013 at 02:47:28PM +0200, Nadav Shemer wrote:
> Some client_expire operations (pnfs_expire_client) may release the state
> lock. To prevent two threads from concurrently expiring the same client,
> the client is unhashed before any other operation

Sorry for the slow response.  Ignoring this for now as it seems to
depend on later pnfs stuff (and I'm a little worried about the idea of
pnfs ops dropping locks).  Resend if I'm confused.

--b.

> 
> Signed-off-by: Nadav Shemer <nadav@primarydata.com>
> ---
> Related to the recent patchset from Benny Halevy, expire_client releases the state lock (expire_client->destroy_client->pnfs_expire_client).
> A different thread processing a SET_CLIENTID/EXCHANGE_ID/etc. might find the client on the confirmed/unconfirmed hash table and also call expire_client on it.
> 
> To correct this, I reshuffled destroy_client to remove the client from hash tables first thing, before the state lock may be released
> 
> Benny: my previous version of this patch had some plays with reference counts (taking a reference for the duration of the destroy).
> In the current version of the tree, destroy_client assumes cl_refcount==0 and is the only caller of free_client besides create_client. So I dropped it
> 
>  fs/nfsd/nfs4state.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
> index b4a28ef..d42434b 100644
> --- a/fs/nfsd/nfs4state.c
> +++ b/fs/nfsd/nfs4state.c
> @@ -1154,57 +1154,60 @@ unhash_client_locked(struct nfs4_client *clp)
>  	list_del(&clp->cl_lru);
>  	spin_lock(&clp->cl_lock);
>  	list_for_each_entry(ses, &clp->cl_sessions, se_perclnt)
>  		list_del_init(&ses->se_hash);
>  	spin_unlock(&clp->cl_lock);
>  }
>  
>  static void
>  destroy_client(struct nfs4_client *clp)
>  {
>  	struct nfs4_openowner *oo;
>  	struct nfs4_delegation *dp;
>  	struct list_head reaplist;
>  	struct nfsd_net *nn = net_generic(clp->net, nfsd_net_id);
>  
> +	list_del(&clp->cl_idhash);
> +	if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
> +		rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
> +	else
> +		rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
> +	spin_lock(&nn->client_lock);
> +	unhash_client_locked(clp);
> +	spin_unlock(&nn->client_lock);
> +
>  	INIT_LIST_HEAD(&reaplist);
>  	spin_lock(&recall_lock);
>  	while (!list_empty(&clp->cl_delegations)) {
>  		dp = list_entry(clp->cl_delegations.next, struct nfs4_delegation, dl_perclnt);
>  		list_del_init(&dp->dl_perclnt);
>  		list_move(&dp->dl_recall_lru, &reaplist);
>  	}
>  	spin_unlock(&recall_lock);
>  	while (!list_empty(&reaplist)) {
>  		dp = list_entry(reaplist.next, struct nfs4_delegation, dl_recall_lru);
>  		destroy_delegation(dp);
>  	}
>  	while (!list_empty(&clp->cl_openowners)) {
>  		oo = list_entry(clp->cl_openowners.next, struct nfs4_openowner, oo_perclient);
>  		release_openowner(oo);
>  	}
>  	pnfs_expire_client(clp);
>  	nfsd4_shutdown_callback(clp);
>  	if (clp->cl_cb_conn.cb_xprt)
>  		svc_xprt_put(clp->cl_cb_conn.cb_xprt);
> -	list_del(&clp->cl_idhash);
> -	if (test_bit(NFSD4_CLIENT_CONFIRMED, &clp->cl_flags))
> -		rb_erase(&clp->cl_namenode, &nn->conf_name_tree);
> -	else
> -		rb_erase(&clp->cl_namenode, &nn->unconf_name_tree);
>  	spin_lock(&nn->client_lock);
> -	unhash_client_locked(clp);
>  	WARN_ON_ONCE(atomic_read(&clp->cl_refcount));
>  	free_client(clp);
>  	spin_unlock(&nn->client_lock);
>  }
>  
>  static void expire_client(struct nfs4_client *clp)
>  {
>  	nfsd4_client_record_remove(clp);
>  	destroy_client(clp);
>  }
>  
>  static void copy_verf(struct nfs4_client *target, nfs4_verifier *source)
>  {
>  	memcpy(target->cl_verifier.data, source->data,
>  			sizeof(target->cl_verifier.data));
> -- 
> 1.8.3.3.754.g9c3c367
> 
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