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

[Zhengyejian (Zetta)]

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@xxxxxxxxxxxxx>
> > > >
> > > > 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@xxxxxxxxxxxxxx>
> > > > Reported-by: Dave Jones <davej@xxxxxxxxxxxxxxxxx>
> > > > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> > > > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> > > > Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > > > Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> > > > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> > > > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> > > > Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
> > > > Link: http://lkml.kernel.org/r/20180122103947.GD2228@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> > > > Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
> > > > Signed-off-by: Zheng Yejian <zhengyejian1@xxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxx>

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;