From: Oleg Nesterov <oleg@redhat.com>
To: lkp@lists.01.org
Subject: Re: kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG: unable to handle kernel paging request at ffffc90000997f18)
Date: Tue, 28 Jun 2016 20:58:54 +0200 [thread overview]
Message-ID: <20160628185853.GA3998@redhat.com> (raw)
In-Reply-To: <20160627170010.GA21628@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 772 bytes --]
On 06/27, Oleg Nesterov wrote:
>
> On 06/27, Andy Lutomirski wrote:
> >
> > Want to send a patch? I could do it, but you understand this code
> > much better than I do.
>
> Well, I'll try to do this tomorrow unless you do it.
I have cloned luto/linux.git to see if kthread_stop() can pin ->stack
somehow, but it seems this is not possible, finish_task_switch() does
free_thread_stack() unconditionally.
Then how (say) proc_pid_stack() can work? If it hits the task which is
alreay dead we are (probably) fine, valid_stack_ptr() should fail iiuc.
But what if we race with the last schedule() ? "addr = *stack" can read
the already vfree'ed memory, no?
Looks like print_context_stack/etc need probe_kernel_address or I missed
something.
Oleg.
WARNING: multiple messages have this Message-ID (diff)
From: Oleg Nesterov <oleg@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
LKP <lkp@01.org>, LKML <linux-kernel@vger.kernel.org>,
kernel test robot <xiaolong.ye@intel.com>
Subject: Re: kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG: unable to handle kernel paging request at ffffc90000997f18)
Date: Tue, 28 Jun 2016 20:58:54 +0200 [thread overview]
Message-ID: <20160628185853.GA3998@redhat.com> (raw)
In-Reply-To: <20160627170010.GA21628@redhat.com>
On 06/27, Oleg Nesterov wrote:
>
> On 06/27, Andy Lutomirski wrote:
> >
> > Want to send a patch? I could do it, but you understand this code
> > much better than I do.
>
> Well, I'll try to do this tomorrow unless you do it.
I have cloned luto/linux.git to see if kthread_stop() can pin ->stack
somehow, but it seems this is not possible, finish_task_switch() does
free_thread_stack() unconditionally.
Then how (say) proc_pid_stack() can work? If it hits the task which is
alreay dead we are (probably) fine, valid_stack_ptr() should fail iiuc.
But what if we race with the last schedule() ? "addr = *stack" can read
the already vfree'ed memory, no?
Looks like print_context_stack/etc need probe_kernel_address or I missed
something.
Oleg.
next prev parent reply other threads:[~2016-06-28 18:58 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-27 5:22 kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG: unable to handle kernel paging request at ffffc90000997f18) Andy Lutomirski
2016-06-27 5:22 ` Andy Lutomirski
2016-06-27 8:28 ` Peter Zijlstra
2016-06-27 8:28 ` Peter Zijlstra
2016-06-27 14:54 ` Oleg Nesterov
2016-06-27 14:54 ` Oleg Nesterov
2016-06-27 15:44 ` Andy Lutomirski
2016-06-27 15:44 ` Andy Lutomirski
2016-06-27 17:00 ` Oleg Nesterov
2016-06-27 17:00 ` Oleg Nesterov
2016-06-28 18:58 ` Oleg Nesterov [this message]
2016-06-28 18:58 ` Oleg Nesterov
2016-06-28 19:12 ` Andy Lutomirski
2016-06-28 19:12 ` Andy Lutomirski
2016-06-28 20:12 ` Oleg Nesterov
2016-06-28 20:12 ` Oleg Nesterov
2016-06-28 20:54 ` Andy Lutomirski
2016-06-28 20:54 ` Andy Lutomirski
2016-06-28 21:14 ` Linus Torvalds
2016-06-28 21:14 ` Linus Torvalds
2016-06-28 21:18 ` Linus Torvalds
2016-06-28 21:18 ` Linus Torvalds
2016-06-28 21:21 ` Andy Lutomirski
2016-06-28 21:21 ` Andy Lutomirski
2016-06-28 21:35 ` Linus Torvalds
2016-06-28 21:35 ` Linus Torvalds
2016-06-28 21:40 ` Linus Torvalds
2016-06-28 21:40 ` Linus Torvalds
2016-06-28 22:47 ` Oleg Nesterov
2016-06-28 22:47 ` Oleg Nesterov
2016-06-28 22:59 ` Oleg Nesterov
2016-06-28 22:59 ` Oleg Nesterov
2016-06-29 15:34 ` Andy Lutomirski
2016-06-29 15:34 ` Andy Lutomirski
2016-06-29 18:03 ` [PATCH] kthread: to_live_kthread() needs try_get_task_stack() Oleg Nesterov
2016-06-29 18:03 ` Oleg Nesterov
2016-06-29 18:28 ` kbuild test robot
2016-06-29 18:28 ` kbuild test robot
2016-06-29 18:44 ` Oleg Nesterov
2016-06-29 18:44 ` Oleg Nesterov
2016-06-29 18:51 ` kbuild test robot
2016-06-29 18:51 ` kbuild test robot
2016-06-29 23:01 ` Andy Lutomirski
2016-06-29 23:01 ` Andy Lutomirski
2016-06-29 23:33 ` kthread_stop insanity (Re: [[DEBUG] force] 2642458962: BUG: unable to handle kernel paging request at ffffc90000997f18) Andy Lutomirski
2016-06-29 23:33 ` Andy Lutomirski
2016-06-27 17:16 ` Linus Torvalds
2016-06-27 17:16 ` Linus Torvalds
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