From: Peter Hurley <peter@hurleysoftware•com>
To: Oleg Nesterov <oleg@redhat•com>
Cc: Sree Harsha Totakura <sreeharsha@totakura•in>,
linux-kernel@vger•kernel.org, netdev@vger•kernel.org
Subject: Re: pppd service crash in linux-3.13.6
Date: Thu, 13 Mar 2014 13:55:31 -0400 [thread overview]
Message-ID: <5321F113.7090000@hurleysoftware.com> (raw)
In-Reply-To: <20140313170622.GA31206@redhat.com>
Hi Oleg,
On 03/13/2014 01:06 PM, Oleg Nesterov wrote:
> On 03/10, Peter Hurley wrote:
>>
>> [ +cc Oleg Nesterov ]
>
> Thanks.
>
>> The NULL ptr dereference is from following the current->nsproxy ptr
>> in ppp_register_channel().
>>
>> This was broken by
>>
>> commit 8aac62706adaaf0fab02c4327761561c8bda9448
>> Author: Oleg Nesterov <oleg@redhat•com>
>> Date: Fri Jun 14 21:09:49 2013 +0200
>>
>> move exit_task_namespaces() outside of exit_notify()
>>
>> which moved the exit_task_namespaces(tsk) before disassociate_ctty().
>
> Heh. OK, we can move it down after disassociate_ctty(), the original
> motivation for that commit was the problem which was also (hopefully)
> fixed by e7b2c406925273 "fput: task_work_add() can fail if the caller
> has passed exit_task_work()".
I didn't look into what motivated the change; I will now though.
> In fact I think that it makes sense to move it down after
> exit_task_work() anyway. But this is almost off-topic and I'd like to
> avoid this right now.
>
> OTOH, why we should delay disassociate_ctty? IOW, do you see any
> potential problem with the trivial patch below?
I have no idea what kind of dependencies might exist between
task works, cgroup_exit() and all the teardown that disassociate_ctty()
does. I'll look into though.
> And it seems that it makes sense to move (at least) check_stack_usage()
> down, but this is offtopic too.
I agree that it makes sense to check the stack _after_ teardown code
runs, but all the arch-dependent exit_thread() code would need to be
audited first.
> Oleg.
>
> --- x/kernel/exit.c
> +++ kernel/exit.c/
> @@ -784,6 +784,8 @@ void do_exit(long code)
> exit_shm(tsk);
> exit_files(tsk);
> exit_fs(tsk);
> + if (group_dead)
> + disassociate_ctty(1);
> exit_task_namespaces(tsk);
> exit_task_work(tsk);
> check_stack_usage();
> @@ -799,13 +801,9 @@ void do_exit(long code)
>
> cgroup_exit(tsk, 1);
>
> - if (group_dead)
> - disassociate_ctty(1);
> -
> module_put(task_thread_info(tsk)->exec_domain->module);
>
> proc_exit_connector(tsk);
> -
> /*
> * FIXME: do that only when needed, using sched_exit tracepoint
> */
Regards,
Peter Hurley
next prev parent reply other threads:[~2014-03-13 17:55 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <531A37FF.4000509@totakura.in>
2014-03-10 16:56 ` pppd service crash in linux-3.13.6 Sree Harsha Totakura
2014-03-10 19:23 ` Peter Hurley
2014-03-13 17:06 ` Oleg Nesterov
2014-03-13 17:55 ` Peter Hurley [this message]
2014-03-14 14:19 ` Peter Hurley
2014-03-14 15:02 ` Peter Hurley
2014-03-14 19:23 ` Oleg Nesterov
2014-03-14 20:28 ` Peter Hurley
2014-03-14 21:04 ` Oleg Nesterov
2014-03-15 12:49 ` Peter Hurley
2014-03-17 18:04 ` [PATCH 0/2] (Was: pppd service crash in linux-3.13.6) Oleg Nesterov
2014-03-17 18:04 ` [PATCH 1/2] exit: call disassociate_ctty() before exit_task_namespaces() Oleg Nesterov
2014-03-17 18:05 ` [PATCH 2/2] exit: move check_stack_usage() to the end of do_exit() Oleg Nesterov
2014-03-10 19:54 ` pppd service crash in linux-3.13.6 Ben Hutchings
2014-03-12 21:25 ` Sree Harsha Totakura
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