Return-Path: linux-nfs-owner@vger.kernel.org Received: from mail-vc0-f174.google.com ([209.85.220.174]:63529 "EHLO mail-vc0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756564AbaHVOtK (ORCPT ); Fri, 22 Aug 2014 10:49:10 -0400 Received: by mail-vc0-f174.google.com with SMTP id la4so12223431vcb.5 for ; Fri, 22 Aug 2014 07:49:09 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <20140822140759.GA31775@ada> References: <20140822140759.GA31775@ada> Date: Fri, 22 Aug 2014 10:49:09 -0400 Message-ID: Subject: Re: [PATCH] nfs: delegation: Replace rcu_assign_pointer() with RCU_INIT_POINTER() From: Trond Myklebust To: Andreea-Cristina Bernat Cc: Linux NFS Mailing List , Linux Kernel mailing list , Paul McKenney Content-Type: text/plain; charset=UTF-8 Sender: linux-nfs-owner@vger.kernel.org List-ID: On Fri, Aug 22, 2014 at 10:07 AM, Andreea-Cristina Bernat wrote: > The use of "rcu_assign_pointer()" is NULLing out the pointer. > According to RCU_INIT_POINTER()'s block comment: > "1. This use of RCU_INIT_POINTER() is NULLing out the pointer" > it is better to use it instead of rcu_assign_pointer() because it has a > smaller overhead. > > The following Coccinelle semantic patch was used: > @@ > @@ > > - rcu_assign_pointer > + RCU_INIT_POINTER > (..., NULL) > > Signed-off-by: Andreea-Cristina Bernat > --- > fs/nfs/delegation.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c > index 5d8ccec..349e63b 100644 > --- a/fs/nfs/delegation.c > +++ b/fs/nfs/delegation.c > @@ -249,7 +249,7 @@ nfs_detach_delegation_locked(struct nfs_inode *nfsi, > list_del_rcu(&delegation->super_list); > delegation->inode = NULL; > nfsi->delegation_state = 0; > - rcu_assign_pointer(nfsi->delegation, NULL); > + RCU_INIT_POINTER(nfsi->delegation, NULL); > spin_unlock(&delegation->lock); > return delegation; > } > -- > 1.9.1 Sorry, but NACK. We do need the memory barriers here, as the nfs_inode is globally visible, and other threads may be checking nfsi->delegation_state and/or delegation->inode in order to conclude whether or not there is still a delegation associated with this inode. Cheers Trond -- Trond Myklebust Linux NFS client maintainer, PrimaryData trond.myklebust@primarydata.com