Date: Mon, 30 Nov 2015 16:16:47 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Zefan Li <lizefan@huawei.com>
Cc: Aleksa Sarai <cyphar@cyphar.com>, Johannes Weiner <hannes@cmpxchg.org>,
        Tejun Heo <tj@kernel.org>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 0/3] cgroup: fix race between cgroup_post_fork() and
	cgroup_migrate()
Message-ID: <20151130151630.GA28046@redhat.com>
References: <20151127185705.GA14669@redhat.com> <56591AED.7050808@huawei.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <56591AED.7050808@huawei.com>
User-Agent: Mutt/1.5.18 (2008-05-17)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1517
Lines: 44

On 11/28, Zefan Li wrote:
>
> On 2015/11/28 2:57, Oleg Nesterov wrote:
>> On 11/26, Oleg Nesterov wrote:
>>>
>>> OK. I do not know what exactly do you mean, perhaps if you fix this problem
>>> the race between fork and attach goes away and in this case the fix I sent
>>> is not needed?
>>
>> Otherwise please consider this series.
>>
>> Slightly tested, seems to work; please review.
>>
>
> Allowing tasks migrating between cgroups while forking is problematic. I'm more
> than glad to see those changes.

Yes, I think this way we can probably do other cleanups/fixes in the generic code
too.

For example, cgroup_enable_task_cg_lists() looks racy, spin_lock_irq(siglock)
can't ensure we can't miss PF_EXITING, exit_signals() doesn't take this lock
in the single-threaded case. We can change it to use cgroup_threadgroup_rwsem
and avoid tasklist_lock afaics.

And I forgot to mention, if we apply this series, we need to rename
threadgroup_change_begin/end and remove the "task_struct *tsk" argument, plus
provide the helpers for write_lock/unlock. Then we can remove
uprobe_start_dup_mmap() and change register_for_each_vma() to use the same
lock.

But I failed to invent the good names for the new helpers ;)

> Acked-by: Zefan Li <lizefan@huawei.com>

Thanks!

Oleg.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/