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Date: Thu, 10 Nov 2022 21:48:54 +1000
Message-Id: <CO8LCA89WZYL.3APIMVZTFJ2QT@bobo>
Subject: Re: [PATCH 04/17] powerpc/qspinlock: convert atomic operations to
 assembly
From: "Nicholas Piggin" <npiggin@gmail.com>
To: "Christophe Leroy" <christophe.leroy@csgroup.eu>, "Jordan Niethe"
 <jniethe5@gmail.com>, "linuxppc-dev@lists.ozlabs.org"
 <linuxppc-dev@lists.ozlabs.org>
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On Thu Nov 10, 2022 at 6:36 PM AEST, Christophe Leroy wrote:
>
>
> Le 10/11/2022 =C3=A0 01:39, Jordan Niethe a =C3=A9crit=C2=A0:
> >> +static __always_inline int trylock_clear_tail_cpu(struct qspinlock *l=
ock, u32 old)
> >>   {
> >> -	int newval =3D _Q_LOCKED_VAL;
> >> -
> >> -	if (atomic_cmpxchg_acquire(&lock->val, val, newval) =3D=3D val)
> >> +	u32 new =3D _Q_LOCKED_VAL;
> >> +	u32 prev;
> >> +
> >> +	BUG_ON(old & _Q_LOCKED_VAL);
> >=20
> > The BUG_ON() could have been introduced in an earlier patch I think.
>
> Can we avoid the BUG_ON() at all and replace by a WARN_ON ?

Lock has gone wrong here. Critical sections not working means data
corruption and little prospect of continuing to run.

Thanks,
Nick