linux-kernel - Re: [PATCH 4.4 3/3] futex: fix dead code in attach_to_pi

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Date:   Wed, 10 Mar 2021 13:00:48 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Zheng Yejian <zhengyejian1@...wei.com>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org, tglx@...utronix.de,
        cj.chengjian@...wei.com, judy.chenhui@...wei.com,
        zhangjinhao2@...wei.com, nixiaoming@...wei.com
Subject: Re: [PATCH 4.4 3/3] futex: fix dead code in attach_to_pi_owner()

On Tue, Mar 09, 2021 at 06:14:37PM +0000, Lee Jones wrote:
> On Tue, 09 Mar 2021, Greg KH wrote:
> 
> > On Tue, Mar 09, 2021 at 11:06:05AM +0800, Zheng Yejian wrote:
> > > From: Thomas Gleixner <tglx@...utronix.de>
> > > 
> > > The handle_exit_race() function is defined in commit 9c3f39860367
> > >  ("futex: Cure exit race"), which never returns -EBUSY. This results
> > > in a small piece of dead code in the attach_to_pi_owner() function:
> > > 
> > > 	int ret = handle_exit_race(uaddr, uval, p); /* Never return -EBUSY */
> > > 	...
> > > 	if (ret == -EBUSY)
> > > 		*exiting = p; /* dead code */
> > > 
> > > The return value -EBUSY is added to handle_exit_race() in upsteam
> > > commit ac31c7ff8624409 ("futex: Provide distinct return value when
> > > owner is exiting"). This commit was incorporated into v4.9.255, before
> > > the function handle_exit_race() was introduced, whitout Modify
> > > handle_exit_race().
> > > 
> > > To fix dead code, extract the change of handle_exit_race() from
> > > commit ac31c7ff8624409 ("futex: Provide distinct return value when owner
> > >  is exiting"), re-incorporated.
> > > 
> > > Lee writes:
> > > 
> > > This commit takes the remaining functional snippet of:
> > > 
> > >  ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")
> > > 
> > > ... and is the correct fix for this issue.
> > > 
> > > Fixes: 9c3f39860367 ("futex: Cure exit race")
> > > Cc: stable@...r.kernel.org # v4.9.258
> > > Signed-off-by: Xiaoming Ni <nixiaoming@...wei.com>
> > > Reviewed-by: Lee Jones <lee.jones@...aro.org>
> > > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Signed-off-by: Zheng Yejian <zhengyejian1@...wei.com>
> > > ---
> > >  kernel/futex.c | 6 +++---
> > >  1 file changed, 3 insertions(+), 3 deletions(-)
> > 
> > Same here, what is the upstream git id?
> 
> It doesn't have one as such - it's a part-patch:
> 
> > > This commit takes the remaining functional snippet of:
> > > 
> > >  ac31c7ff8624409 ("futex: Provide distinct return value when owner is exiting")

That wasn't obvious :(

Is this a backport of another patch in the stable tree somewhere?

confused,

greg k-h