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

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Date:   Thu, 25 Feb 2021 08:09:30 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     "Zhengyejian (Zetta)" <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 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>

> > > ---
> > >   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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