linux-kernel - Re: [PATCH 4.4 3/3] futex: fix dead code in attach_to_pi

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Date:   Thu, 11 Mar 2021 09:39:19 +0800
From:   "Zhengyejian (Zetta)" <zhengyejian1@...wei.com>
To:     Greg KH <gregkh@...uxfoundation.org>,
        Lee Jones <lee.jones@...aro.org>, <stable@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
        <cj.chengjian@...wei.com>, <judy.chenhui@...wei.com>,
        <zhangjinhao2@...wei.com>, <nixiaoming@...wei.com>
Subject: Re: [PATCH 4.4 3/3] futex: fix dead code in attach_to_pi_owner()



On 2021/3/10 22:10, Greg KH wrote:
> On Wed, Mar 10, 2021 at 01:28:02PM +0000, Lee Jones wrote:
>> On Wed, 10 Mar 2021, Greg KH wrote:
>>
>>> On Tue, Mar 09, 2021 at 06:14:37PM +0000, Lee Jones wrote:
>>>> On Tue, 09 Mar 2021, Greg KH wrote:
>>>>
>>>>> On Tue, Mar 09, 2021 at 11:06:05AM +0800, Zheng Yejian wrote:
>>>>>> From: Thomas Gleixner <tglx@...utronix.de>
>>>>>>
>>>>>> The handle_exit_race() function is defined in commit 9c3f39860367
>>>>>>   ("futex: Cure exit race"), which never returns -EBUSY. This results
>>>>>> in a small piece of dead code in the attach_to_pi_owner() function:
>>>>>>
>>>>>> 	int ret = handle_exit_race(uaddr, uval, p); /* Never return -EBUSY */
>>>>>> 	...
>>>>>> 	if (ret == -EBUSY)
>>>>>> 		*exiting = p; /* dead code */
>>>>>>
>>>>>> The return value -EBUSY is added to handle_exit_race() in upsteam
>>>>>> commit ac31c7ff8624409 ("futex: Provide distinct return value when
>>>>>> owner is exiting"). This commit was incorporated into v4.9.255, before
>>>>>> the function handle_exit_race() was introduced, whitout Modify
>>>>>> handle_exit_race().
>>>>>>
>>>>>> To fix dead code, extract the change of handle_exit_race() from
>>>>>> commit ac31c7ff8624409 ("futex: Provide distinct return value when owner
>>>>>>   is exiting"), re-incorporated.
>>>>>>
>>>>>> Lee writes:
>>>>>>
>>>>>> This commit takes the remaining functional snippet of:
>>>>>>
>>>>>>   ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")
>>>>>>
>>>>>> ... and is the correct fix for this issue.
>>>>>>
>>>>>> Fixes: 9c3f39860367 ("futex: Cure exit race")
>>>>>> Cc: stable@...r.kernel.org # v4.9.258
>>>>>> Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
>>>>>> Reviewed-by: Lee Jones <lee.jones@...aro.org>
>>>>>> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>>>> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
>>>>>> ---
>>>>>>   kernel/futex.c | 6 +++---
>>>>>>   1 file changed, 3 insertions(+), 3 deletions(-)
>>>>>
>>>>> Same here, what is the upstream git id?
>>>>
>>>> It doesn't have one as such - it's a part-patch:
>>>>
>>>>>> This commit takes the remaining functional snippet of:
>>>>>>
>>>>>>   ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")
>>>
>>> That wasn't obvious :(
>>
>> This was also my thinking, which is why I replied to the original
>> patch in an attempt to clarify what I thought was happening.
>>
>>> Is this a backport of another patch in the stable tree somewhere?
>>
>> Yes, it looks like it.
>>
>> The full patch was back-ported to v4.14 as:
>>
>>    e6e00df182908f34360c3c9f2d13cc719362e9c0
> 
> Ok, Zheng, can you put this information in the patch and resend the
> whole series?
> 

Sure, I'll send a "v2" patchset soon.
Thanks for your suggestions,

Zheng Yejian