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Subject: Re: [PATCH stable-rc queue/4.9 1/1] futex: Provide distinct return
 value when owner is exiting
To:     Greg KH <gregkh@linuxfoundation.org>
CC:     <linux-kernel@vger.kernel.org>, <stable@vger.kernel.org>,
        <sashal@kernel.org>, <tglx@linutronix.de>, <wangle6@huawei.com>,
        <zhengyejian1@huawei.com>
References: <20210222070328.102384-1-nixiaoming@huawei.com>
 <20210222070328.102384-2-nixiaoming@huawei.com> <YDOEZhmKqjTVxtMn@kroah.com>
From:   Xiaoming Ni <nixiaoming@huawei.com>
Message-ID: <3bc570f6-f8af-b0a2-4d62-13ed4adc1f33@huawei.com>
Date:   Mon, 22 Feb 2021 18:54:06 +0800
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On 2021/2/22 18:16, Greg KH wrote:
> On Mon, Feb 22, 2021 at 03:03:28PM +0800, Xiaoming Ni wrote:
>> From: Thomas Gleixner<tglx@linutronix.de>
>>
>> commit ac31c7ff8624409ba3c4901df9237a616c187a5d upstream.
> This commit is already in the 4.9 tree.  If the backport was incorrect,
> say that here, and describe what went wrong and why this commit fixes
> it.
> 
> Also state what commit this fixes as well, otherwise this changelog just
> looks like it is being applied again to the tree, which doesn't make
> much sense.
> 
> thanks,
> 
> greg k-h
> .

I wrote a cover for it. but forgot to adjust the title of the cover:
 
https://lore.kernel.org/lkml/20210222070328.102384-1-nixiaoming@huawei.com/


I found a dead code in the queue/4.9 branch of the stable-rc repository.

2021-02-03:
commit c27f392040e2f6 ("futex: Provide distinct return value when
  owner is exiting")
	The function handle_exit_race does not exist. Therefore, the
	change in handle_exit_race() is ignored in the patch round.

2021-02-22:
commit e55cb811e612 ("futex: Cure exit race")
	Define the handle_exit_race() function,
	but no branch in the function returns EBUSY.
	As a result, dead code occurs in the attach_to_pi_owner():

		int ret = handle_exit_race(uaddr, uval, p);
		...
		if (ret == -EBUSY)
			*exiting = p; /* dead code */

To fix the dead code, modify the commit e55cb811e612 ("futex: Cure exit 
race"),
or install a patch to incorporate the changes in handle_exit_race().

I am unfamiliar with the processing of the stable-rc queue branch,
and I cannot find the patch mail of the current branch in
	https://lore.kernel.org/lkml/?q=%22futex%3A+Cure+exit+race%22
Therefore, I re-integrated commit ac31c7ff8624 ("futex: Provide distinct
  return value when owner is exiting").
  And wrote a cover (but forgot to adjust the title of the cover):
 
https://lore.kernel.org/lkml/20210222070328.102384-1-nixiaoming@huawei.com/

Thanks
Xiaoming Ni