From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754522AbZBCTlv (ORCPT ); Tue, 3 Feb 2009 14:41:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752133AbZBCTlm (ORCPT ); Tue, 3 Feb 2009 14:41:42 -0500 Received: from mx2.redhat.com ([66.187.237.31]:39454 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752142AbZBCTlm (ORCPT ); Tue, 3 Feb 2009 14:41:42 -0500 Date: Tue, 3 Feb 2009 20:39:04 +0100 From: Oleg Nesterov To: Ingo Molnar , Steven Rostedt Cc: "Eric W. Biederman" , linux-kernel@vger.kernel.org Subject: [PATCH] ftrace: do_each_pid_task() needs rcu lock Message-ID: <20090203193904.GA23695@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "ftrace: use struct pid" commit 978f3a45d9499c7a447ca7615455cefb63d44165 converted ftrace_pid_trace to "struct pid*". But we can't use do_each_pid_task() without rcu_read_lock() even if we know the pid itself can't go away (it was pinned in ftrace_pid_write). The exiting task can detach itself from this pid at any moment. Signed-off-by: Oleg Nesterov --- 6.29-rc3/kernel/trace/ftrace.c~FTRACE_PID 2009-01-12 23:07:51.000000000 +0100 +++ 6.29-rc3/kernel/trace/ftrace.c 2009-02-03 20:23:59.000000000 +0100 @@ -1736,9 +1736,12 @@ static void clear_ftrace_pid(struct 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); } @@ -1746,9 +1749,11 @@ static void set_ftrace_pid(struct pid *p { struct task_struct *p; + rcu_read_lock(); do_each_pid_task(pid, PIDTYPE_PID, p) { set_tsk_trace_trace(p); } while_each_pid_task(pid, PIDTYPE_PID, p); + rcu_read_unlock(); } static void clear_ftrace_pid_task(struct pid **pid)