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

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Message-ID: <20210224111915.GA641347@dell>
Date:   Wed, 24 Feb 2021 11:19:15 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Zheng Yejian <zhengyejian1@...wei.com>
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 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?

> ---
>  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;

-- 
Lee Jones [李琼斯]
Senior Technical Lead - Developer Services
Linaro.org │ Open source software for Arm SoCs
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