From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH] net/core: Use RCU_INIT_POINTER(x, NULL) in netpoll.c Date: Thu, 27 Mar 2014 14:28:31 -0700 Message-ID: <20140327212831.GA4284@linux.vnet.ibm.com> References: <1395601966-12490-1-git-send-email-monamagarwal123@gmail.com> <20140324111144.GA19368@hmsreliant.think-freely.org> Reply-To: paulmck@linux.vnet.ibm.com Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Monam Agarwal , davem@davemloft.net, ebiederm@xmission.com, cwang@twopensource.com, kaber@trash.net, antonio@meshcoding.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Neil Horman Return-path: Content-Disposition: inline In-Reply-To: <20140324111144.GA19368@hmsreliant.think-freely.org> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Mon, Mar 24, 2014 at 07:11:44AM -0400, Neil Horman wrote: > On Mon, Mar 24, 2014 at 12:42:46AM +0530, Monam Agarwal wrote: > > This patch replaces rcu_assign_pointer(x, NULL) with RCU_INIT_POINTER(x, NULL) > > > > The rcu_assign_pointer() ensures that the initialization of a structure > > is carried out before storing a pointer to that structure. > > And in the case of the NULL pointer, there is no structure to initialize. > > So, rcu_assign_pointer(p, NULL) can be safely converted to RCU_INIT_POINTER(p, NULL) > > > > Signed-off-by: Monam Agarwal > No, I don't think this is right. __netpoll_cleanup can be called in parallel > with bottom half access to dev->npinfo. rcu_assign pointer is safe against > those accesses, but RCU_INIT_POINTER is not. Hello, Neil, But in this case, NULL is being assigned, so there should be no problem. If this was a non-NULL pointer to a structure that had not already been exposed to readers, then yes, this would be a problem. But NULL pointers are OK to assign using RCU_INIT_POINTER(). Thanx, Paul > Neil > > > --- > > net/core/netpoll.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/net/core/netpoll.c b/net/core/netpoll.c > > index 7291dde..41c4e9c 100644 > > --- a/net/core/netpoll.c > > +++ b/net/core/netpoll.c > > @@ -809,7 +809,7 @@ void __netpoll_cleanup(struct netpoll *np) > > if (ops->ndo_netpoll_cleanup) > > ops->ndo_netpoll_cleanup(np->dev); > > > > - rcu_assign_pointer(np->dev->npinfo, NULL); > > + RCU_INIT_POINTER(np->dev->npinfo, NULL); > > call_rcu_bh(&npinfo->rcu, rcu_cleanup_netpoll_info); > > } > > } > > -- > > 1.7.9.5 > > > > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ >