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

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Message-ID: <CAFULd4bt5oiQq4_3jSDe+3P=1xtAhZ=34vLREqPVT9njjdWKSA@mail.gmail.com>
Date: Fri, 19 Jul 2024 12:15:28 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: Bibo Mao <maobibo@...ngson.cn>
Cc: Will Deacon <will@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Boqun Feng <boqun.feng@...il.com>, 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 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;
       /*
        * 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.