From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753016AbaKKKjx (ORCPT ); Tue, 11 Nov 2014 05:39:53 -0500 Received: from casper.infradead.org ([85.118.1.10]:36263 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752684AbaKKKjw (ORCPT ); Tue, 11 Nov 2014 05:39:52 -0500 Date: Tue, 11 Nov 2014 11:39:49 +0100 From: Peter Zijlstra To: Oleg Nesterov Cc: Andrew Morton , Aaron Tomlin , "Eric W. Biederman" , Roland McGrath , Sterling Alexander , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/5] sched_show_task: fix unsafe usage of ->real_parent Message-ID: <20141111103949.GK10501@worktop.programming.kicks-ass.net> References: <20141110215959.GA31106@redhat.com> <20141110220026.GA31224@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20141110220026.GA31224@redhat.com> User-Agent: Mutt/1.5.22.1 (2013-10-16) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 10, 2014 at 11:00:26PM +0100, Oleg Nesterov wrote: > rcu_read_lock() can not protect p->real_parent if release_task(p) was > already called, change sched_show_task() to check pis_alive() like > other users do. > > Note: we need some helpers to cleanup the code like this. And it seems > that that the usage of cpu_curr(cpu) in dump_cpu_task() is not safe too. > > Signed-off-by: Oleg Nesterov Acked-by: Peter Zijlstra (Intel) > --- > kernel/sched/core.c | 4 +++- > 1 files changed, 3 insertions(+), 1 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 240157c..1ec75c9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4572,8 +4572,10 @@ void sched_show_task(struct task_struct *p) > #ifdef CONFIG_DEBUG_STACK_USAGE > free = stack_not_used(p); > #endif > + ppid = 0; > rcu_read_lock(); > - ppid = task_pid_nr(rcu_dereference(p->real_parent)); > + if (pid_alive(p)) > + ppid = task_pid_nr(rcu_dereference(p->real_parent)); > rcu_read_unlock(); > printk(KERN_CONT "%5lu %5d %6d 0x%08lx\n", free, > task_pid_nr(p), ppid, > -- > 1.5.5.1 >