linux-kernel - Re: [PATCH] locking/atomic: scripts: Fix type error in macro try

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Message-ID: <ZpqR4qkFUNgkJj0x@boqun-archlinux>
Date: Fri, 19 Jul 2024 09:18:42 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Uros Bizjak <ubizjak@...il.com>
Cc: Bibo Mao <maobibo@...ngson.cn>, Will Deacon <will@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>,
	"Paul E . McKenney" <paulmck@...nel.org>,
	Carlos Llamas <cmllamas@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/atomic: scripts: Fix type error in macro
 try_cmpxchg

On Fri, Jul 19, 2024 at 12:15:28PM +0200, Uros Bizjak wrote:
> On Fri, Jul 19, 2024 at 4:40 AM Bibo Mao <maobibo@...ngson.cn> wrote:
> >
> > When porting pv spinlock function on LoongArch system, there is
> > compiling error such as:
> >                  from linux/include/linux/smp.h:13,
> >                  from linux/kernel/locking/qspinlock.c:16:
> > linux/kernel/locking/qspinlock_paravirt.h: In function 'pv_kick_node':
> > linux/include/linux/atomic/atomic-arch-fallback.h:242:34: error: initialization of 'u8 *' {aka 'unsigned char *'} from incompatible pointer type 'enum vcpu_state *' [-Wincompatible-pointer-types]
> >   242 |         typeof(*(_ptr)) *___op = (_oldp), ___o = *___op, ___r; \
> >       |                                  ^
> > linux/atomic/atomic-instrumented.h:4908:9: note: in expansion of macro 'raw_try_cmpxchg_relaxed'
> >  4908 |         raw_try_cmpxchg_relaxed(__ai_ptr, __ai_oldp, __VA_ARGS__); \
> >       |         ^~~~~~~~~~~~~~~~~~~~~~~
> > linux/kernel/locking/qspinlock_paravirt.h:377:14: note: in expansion of macro 'try_cmpxchg_relaxed'
> >   377 |         if (!try_cmpxchg_relaxed(&pn->state, &old, vcpu_hashed))
> 
> This points to the mismatch between "pn->state" and "old" variable.
> The correct fix is:
> 
> --cut here--
> diff --git a/kernel/locking/qspinlock_paravirt.h
> b/kernel/locking/qspinlock_paravirt.h
> index f5a36e67b593..ac2e22502741 100644
> --- a/kernel/locking/qspinlock_paravirt.h
> +++ b/kernel/locking/qspinlock_paravirt.h
> @@ -357,7 +357,7 @@ static void pv_wait_node(struct mcs_spinlock
> *node, struct mcs_spinlock *prev)
> static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
> {
>        struct pv_node *pn = (struct pv_node *)node;
> -       enum vcpu_state old = vcpu_halted;
> +       u8 old = vcpu_halted;
>        /*

Looks reasonable to me, we should also add static_assert() for
try_cmpxhg_*() to make sure the old has the same size of the cmpxchged
field.

Regards,
Boqun

>         * If the vCPU is indeed halted, advance its state to match that of
>         * pv_wait_node(). If OTOH this fails, the vCPU was running and will
> --cut here--
> 
> Uros.