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Re: [PATCH 0/3] cgroup: fix race between cgroup_post_fork() and cgroup_migrate()

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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.

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[PATCH 0/3] cgroup: fix race between cgroup_post_fork() and  cgroup_migrate() Oleg Nesterov <oleg@redhat.com> - 2015-11-27 20:00 +0100
  [PATCH 1/3] cgroup: pids: fix race between cgroup_post_fork() and  cgroup_migrate() Oleg Nesterov <oleg@redhat.com> - 2015-11-27 20:00 +0100
  [PATCH 2/3] cgroup: pids: kill pids_fork(), simplify  pids_can_fork() and pids_cancel_fork() Oleg Nesterov <oleg@redhat.com> - 2015-11-27 20:00 +0100
  [PATCH 3/3] cgroup: kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] and  friends Oleg Nesterov <oleg@redhat.com> - 2015-11-27 20:00 +0100
    Re: [PATCH 3/3] cgroup: kill cgrp_ss_priv[CGROUP_CANFORK_COUNT] and  friends Tejun Heo <tj@kernel.org> - 2015-12-03 16:20 +0100
  Re: [PATCH 0/3] cgroup: fix race between cgroup_post_fork() and  cgroup_migrate() Zefan Li <lizefan@huawei.com> - 2015-11-28 04:20 +0100
    Re: [PATCH 0/3] cgroup: fix race between cgroup_post_fork() and  cgroup_migrate() Oleg Nesterov <oleg@redhat.com> - 2015-11-30 16:20 +0100
  Re: [PATCH 0/3] cgroup: fix race between cgroup_post_fork() and  cgroup_migrate() Tejun Heo <tj@kernel.org> - 2015-11-30 16:00 +0100

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