Return-Path: Received: from mail-qg0-f42.google.com ([209.85.192.42]:33843 "EHLO mail-qg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755395AbcDNMhQ (ORCPT ); Thu, 14 Apr 2016 08:37:16 -0400 Received: by mail-qg0-f42.google.com with SMTP id c6so61699161qga.1 for ; Thu, 14 Apr 2016 05:37:15 -0700 (PDT) From: Jeff Layton To: trond.myklebust@primarydata.com Cc: linux-nfs@vger.kernel.org Subject: [PATCH 4/8] sunrpc: add a get_rpccred_rcu inline Date: Thu, 14 Apr 2016 08:37:01 -0400 Message-Id: <1460637425-1580-5-git-send-email-jeff.layton@primarydata.com> In-Reply-To: <1460637425-1580-1-git-send-email-jeff.layton@primarydata.com> References: <1460637425-1580-1-git-send-email-jeff.layton@primarydata.com> Sender: linux-nfs-owner@vger.kernel.org List-ID: Sometimes we might have a RCU managed credential pointer and don't want to use locking to handle it. Add a function that will take a reference to the cred iff the refcount is not already zero. Callers can dereference the pointer under the rcu_read_lock and use that function to take a reference only if the cred is not on its way to destruction. Signed-off-by: Jeff Layton --- include/linux/sunrpc/auth.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/linux/sunrpc/auth.h b/include/linux/sunrpc/auth.h index 16bd8f8fef8c..6f36b2bf3e05 100644 --- a/include/linux/sunrpc/auth.h +++ b/include/linux/sunrpc/auth.h @@ -206,5 +206,23 @@ struct rpc_cred * get_rpccred(struct rpc_cred *cred) return cred; } +/** + * get_rpccred_rcu - get a reference to a cred using rcu-protected pointer + * @cred: cred of which to take a reference + * + * In some cases, we may have a pointer to a credential to which we + * want to take a reference, but don't already have one. Because these + * objects are freed using RCU, we can access the cr_count while its + * on its way to destruction and only take a reference if it's not already + * zero. + */ +static inline struct rpc_cred * +get_rpccred_rcu(struct rpc_cred *cred) +{ + if (atomic_inc_not_zero(&cred->cr_count)) + return cred; + return NULL; +} + #endif /* __KERNEL__ */ #endif /* _LINUX_SUNRPC_AUTH_H */ -- 2.5.5