Re: [PATCH 4.9.y 1/1] futex: Fix OWNER_DEAD fixup

From: Lee Jones <lee.jones@linaro.org>
To: Zheng Yejian <zhengyejian1@huawei.com>
Cc: gregkh@linuxfoundation.org, stable@vger.kernel.org,
	linux-kernel@vger.kernel.org, tglx@linutronix.de,
	cj.chengjian@huawei.com, judy.chenhui@huawei.com,
	zhangjinhao2@huawei.com
Subject: Re: [PATCH 4.9.y 1/1] futex: Fix OWNER_DEAD fixup
Date: Wed, 24 Feb 2021 11:19:15 +0000	[thread overview]
Message-ID: <20210224111915.GA641347@dell> (raw)
In-Reply-To: <20210223144151.916675-2-zhengyejian1@huawei.com>

On Tue, 23 Feb 2021, Zheng Yejian wrote:

> From: Peter Zijlstra <peterz@infradead.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@linux-m68k.org>
> Reported-by: Dave Jones <davej@codemonkey.org.uk>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Paul E. McKenney <paulmck@us.ibm.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.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@kernel.org>
> Signed-off-by: Zheng Yejian <zhengyejian1@huawei.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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