Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758131AbYLDO3W (ORCPT ); Thu, 4 Dec 2008 09:29:22 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757970AbYLDO3H (ORCPT ); Thu, 4 Dec 2008 09:29:07 -0500 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:51637 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754524AbYLDO3F (ORCPT ); Thu, 4 Dec 2008 09:29:05 -0500 Date: Thu, 4 Dec 2008 09:29:04 -0500 (EST) From: Steven Rostedt X-X-Sender: rostedt@gandalf.stny.rr.com To: Dave Hansen cc: "Eric W. Biederman" , Frederic Weisbecker , linux-kernel@vger.kernel.org, Steven Rostedt , containers@lists.osdl.org, Ingo Molnar , Sukadev Bhattiprolu , Andrew Morton Subject: Re: [PATCH 2/3] ftrace: use struct pid In-Reply-To: <1228396022.13111.27.camel@nimitz> Message-ID: References: <20081204052638.425740534@goodmis.org> <20081204052735.175697908@goodmis.org> <1228395378.13111.23.camel@nimitz> <1228396022.13111.27.camel@nimitz> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1511 Lines: 42 On Thu, 4 Dec 2008, Dave Hansen wrote: > On Thu, 2008-12-04 at 04:56 -0800, Dave Hansen wrote: > > On Thu, 2008-12-04 at 04:42 -0800, Eric W. Biederman wrote: > > > > > > > +static void clear_ftrace_pid_task(struct pid **pid) > > > > +{ > > > > + struct task_struct *p; > > > > + > > > rcu_read_lock(); > > > > > > > + do_each_pid_task(*pid, PIDTYPE_PID, p) { > > > > + clear_tsk_trace_trace(p); > > > > + } while_each_pid_task(*pid, PIDTYPE_PID, p); > > > rcu_read_unlock() > > > > > > > + put_pid(*pid); > > > > + > > > > + *pid = NULL; > > > > +} > > > > Could we get away with sticking the rcu_read_{un}lock() inside those > > macros? Those are going to get used in pretty high level code and we're > > allowed to nest rcu_read_lock(). No danger of deadlocks or lock > > inversions. > > Why don't any of the other users of do_each_pid_task() use > rcu_read_lock()? They all seem to be under read_lock(&tasklist_lock) > (except one is under a write lock of the same). Well, if the pid hashes are traversal safe (rcu style), then we only worry about a node or task being freed. I'm assuming that the node is protected via RCU as tasks are, then using only rcu_read_lock should be sufficient. -- Steve -- 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/