Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262068AbVDLJMS (ORCPT ); Tue, 12 Apr 2005 05:12:18 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262070AbVDLJMS (ORCPT ); Tue, 12 Apr 2005 05:12:18 -0400 Received: from mx1.redhat.com ([66.187.233.31]:59529 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S262068AbVDLJMM (ORCPT ); Tue, 12 Apr 2005 05:12:12 -0400 From: David Howells In-Reply-To: <20050411224500.GB1304@us.ibm.com> References: <20050411224500.GB1304@us.ibm.com> <29204.1111608899@redhat.com> <29827.1111611346@redhat.com> To: paulmck@us.ibm.com Cc: torvalds@osdl.org, akpm@osdl.org, Michael A Halcrow , linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/3] Keys: Use RCU to manage session keyring pointer X-Mailer: MH-E 7.82; nmh 1.0.4; GNU Emacs 21.3.50.1 Date: Tue, 12 Apr 2005 10:11:50 +0100 Message-ID: <31445.1113297110@redhat.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1527 Lines: 44 Paul E. McKenney wrote: > > spin_lock_irqsave(&tsk->sighand->siglock, flags); > > - old = tsk->signal->session_keyring; > > - tsk->signal->session_keyring = keyring; > > + old = rcu_dereference(tsk->signal->session_keyring); > > I don't understand why rcu_dereference() is needed in this case. > Since we are holding the lock, it should not be possible for > this to change, right? Or am I missing something? (Quite possible, > am not all that familiar with this code.) Erm... you're right. I stuck the rcu_dereference() in then added the locks back in when I realised I still needed them. > > + synchronize_kernel(); > > This would want to become synchronize_rcu(). I think the deprecation happened since I wrote my patch. > > + if (tsk->signal->session_keyring) { > > + rcu_read_lock(); > > + key = keyring_search_aux( > > + rcu_dereference(tsk->signal->session_keyring), > > + type, description, match); > > + rcu_read_unlock(); > > + } > > + else { > > + key = keyring_search_aux(tsk->user->session_keyring, > > + type, description, match); > > This one is constant, right? If not, I don't understand the locking design. Which one? tsk->user->session_keyring is, tsk->signal->session_keyring is not. Thanks for the review. David - 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/