linux-kernel - Re: [PATCH 4.9.y 1/1] futex: Fix OWNER

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Date:   Thu, 25 Feb 2021 16:50:45 +0800
From:   "Zhengyejian (Zetta)" <zhengyejian1@...wei.com>
To:     Lee Jones <lee.jones@...aro.org>
CC:     <gregkh@...uxfoundation.org>, <stable@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <tglx@...utronix.de>,
        <cj.chengjian@...wei.com>, <judy.chenhui@...wei.com>,
        <zhangjinhao2@...wei.com>
Subject: Re: [PATCH 4.9.y 1/1] futex: Fix OWNER_DEAD fixup



On 2021/2/25 16:09, Lee Jones wrote:
> On Thu, 25 Feb 2021, Zhengyejian (Zetta) wrote:
> 
>>
>>
>> On 2021/2/24 19:19, Lee Jones wrote:
>>> On Tue, 23 Feb 2021, Zheng Yejian wrote:
>>>
>>>> From: Peter Zijlstra <peterz@...radead.org>
>>>>
>>>> commit a97cb0e7b3f4c6297fd857055ae8e895f402f501 upstream.
>>>>
>>>> Both Geert and DaveJ reported that the recent futex commit:
>>>>
>>>>     c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
>>>>
>>>> introduced a problem with setting OWNER_DEAD. We set the bit on an
>>>> uninitialized variable and then entirely optimize it away as a
>>>> dead-store.
>>>>
>>>> Move the setting of the bit to where it is more useful.
>>>>
>>>> Reported-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>>>> Reported-by: Dave Jones <davej@...emonkey.org.uk>
>>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
>>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>>> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
>>>> Cc: Paul E. McKenney <paulmck@...ibm.com>
>>>> Cc: Peter Zijlstra <peterz@...radead.org>
>>>> Cc: Thomas Gleixner <tglx@...utronix.de>
>>>> Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
>>>> Link: http://lkml.kernel.org/r/20180122103947.GD2228@hirez.programming.kicks-ass.net
>>>> Signed-off-by: Ingo Molnar <mingo@...nel.org>
>>>> Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
>>>
>>> Why have you dropped my Reviewed-by?
>>>
>> Really sorry. I thought that a changed patchset needs another review.
>> Then I do need to append your Reviewed-by and send a "V2" patchset, Do I?
> 
> No need.  I won't hold up merging just for that.
> 
> Just bear in mind that you should apply and carry forward *-by tags
> unless there have been significant/functional changes.
> 
> Reviewed-by: Lee Jones <lee.jones@...aro.org>
> 

I get it, thanks.

>>>> ---
>>>>    kernel/futex.c | 6 +++---
>>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/kernel/futex.c b/kernel/futex.c
>>>> index b65dbb5d60bb..604d1cb9839d 100644
>>>> --- a/kernel/futex.c
>>>> +++ b/kernel/futex.c
>>>> @@ -2424,9 +2424,6 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
>>>>    	int err = 0;
>>>>    	oldowner = pi_state->owner;
>>>> -	/* Owner died? */
>>>> -	if (!pi_state->owner)
>>>> -		newtid |= FUTEX_OWNER_DIED;
>>>>    	/*
>>>>    	 * We are here because either:
>>>> @@ -2484,6 +2481,9 @@ static int __fixup_pi_state_owner(u32 __user *uaddr, struct futex_q *q,
>>>>    	}
>>>>    	newtid = task_pid_vnr(newowner) | FUTEX_WAITERS;
>>>> +	/* Owner died? */
>>>> +	if (!pi_state->owner)
>>>> +		newtid |= FUTEX_OWNER_DIED;
>>>>    	if (get_futex_value_locked(&uval, uaddr))
>>>>    		goto handle_fault;
>>>
>