From: Oleg Nesterov <oleg@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: Fengguang Wu <fengguang.wu@intel.com>,
LKML <linux-kernel@vger.kernel.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>
Subject: Re: yama_ptrace_access_check(): possible recursive locking detected
Date: Wed, 15 Aug 2012 15:01:59 +0200 [thread overview]
Message-ID: <20120815130159.GA3221@redhat.com> (raw)
In-Reply-To: <CAGXu5j+0FUYdBqsotn_vp1EbG=dcURAA1sxv+yFzaJuUkdAh0A@mail.gmail.com>
On 08/14, Kees Cook wrote:
>
> Okay, I've now managed to reproduce this locally. I added a bunch of
> debugging, and I think I understand what's going on. This warning is,
> actually, a false positive.
Sure. I mean that yes, this warning doesn't mean we already hit deadlock.
> get used recursively (the task_struct->alloc_lock), but they are
> separate instantiations ("task" is never "current").
Yes. But suppose that we have 2 tasks T1 and T2,
- T1 does ptrace(PTRACE_ATTACH, T2);
- T2 does ptrace(PTRACE_ATTACH, T1);
at the same time. This can lead to the "real" deadlock, no?
> So Oleg's suggestion of removing the locking around the reading of
> ->comm is wrong since it really does need the lock.
Nothing bad can happen without the lock. Yes, printk() can print
some string "in between" if we race with set_task_comm() but this
is all.
BTW, set_task_comm()->wmb() and memset() should die. There are
not needed afaics, and the comment is misleading.
Oleg.
next prev parent reply other threads:[~2012-08-15 13:05 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-07-26 13:47 yama_ptrace_access_check(): possible recursive locking detected Fengguang Wu
2012-07-26 15:41 ` Oleg Nesterov
2012-07-30 17:00 ` Kees Cook
2012-08-10 1:39 ` Kees Cook
2012-08-10 1:52 ` Fengguang Wu
2012-08-14 21:16 ` Kees Cook
2012-08-15 3:01 ` Fengguang Wu
2012-08-15 5:56 ` Kees Cook
2012-08-15 8:05 ` Peter Zijlstra
2012-08-15 13:01 ` Oleg Nesterov [this message]
2012-08-15 14:30 ` Peter Zijlstra
2012-08-15 17:56 ` Oleg Nesterov
2012-08-15 18:09 ` Kees Cook
2012-08-15 18:17 ` Oleg Nesterov
2012-08-15 18:30 ` Kees Cook
2012-08-15 18:44 ` Alan Cox
2012-08-15 18:43 ` Kees Cook
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