Re: double call identical release when there is a race hitting

From	zhong jiang <zhongjiang@huawei.com>
Newsgroups	linux.kernel
Subject	Re: double call identical release when there is a race hitting
Date	2017-06-07 04:30 +0200
Message-ID	<tPyTn-qL-3@gated-at.bofh.it> (permalink)
References	<tPn1T-12m-5@gated-at.bofh.it> <tPp3H-2jT-3@gated-at.bofh.it>
Organization	linux.* mail to news gateway

Show all headers | View raw

On 2017/6/6 23:56, Oleg Nesterov wrote:
> I can't answer authoritatively, but
>
> On 06/06, zhong jiang wrote:
>> Hi
>>
>> when I review the code, I find the following scenario will lead to a race ,
>> but I am not sure whether the real issue will hit or not.
>>
>> cpu1                                                                      cpu2
>> exit_mmap                                               mmu_notifier_unregister
>>    __mmu_notifier_release                                 srcu_read_lock
>>             srcu_read_lock
>>             mm->ops->release(mn, mm)                 mm->ops->release(mn,mm)
>>            srcu_read_unlock                                         srcu_read_unlock
>>
>>
>> obviously,  the specified mm will call identical release function when
>> the related condition satisfy.  is it right?
> I think you are right, this is possible, perhaps the comments should mention
> this explicitly.
>
> See the changelog in d34883d4e35c0a994e91dd847a82b4c9e0c31d83 "mm: mmu_notifier:
> re-fix freed page still mapped in secondary MMU":
>
> 	"multiple ->release() callouts", we needn't care it too much ...
>
> Oleg.
>
>
> .
>
Thank you for clarification.
 yes,  I see that the author admit that this is a issue.   The patch describe that it is really rare.
 Anyway, this issue should be fixed in a separate patch.

but so far  the issue still exist unfortunately.

Regards
zhongjiang

Back to linux.kernel | Previous | Next — Previous in thread | Find similar | Unroll thread

Thread

double call identical release when there is a race hitting zhong jiang <zhongjiang@huawei.com> - 2017-06-06 15:50 +0200
  Re: double call identical release when there is a race hitting Oleg Nesterov <oleg@redhat.com> - 2017-06-06 18:00 +0200
    Re: double call identical release when there is a race hitting zhong jiang <zhongjiang@huawei.com> - 2017-06-07 04:30 +0200

csiph-web