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From: "Paul E. McKenney" <paulmck@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Bradley Morgan <brads@mainlining.org>,
	Vineet Gupta <vgupta@kernel.org>, Guo Ren <guoren@kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arnd Bergmann <arnd@kernel.org>,
	David Laight <david.laight.linux@gmail.com>,
	linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org,
	linux-sh@vger.kernel.org, kernel-team@meta.com,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH 3/5] ARC: Emulate two-byte cmpxchg
Date: Wed,  7 Oct 2026 13:36:34 -0700	[thread overview]
Message-ID: <20261007203636.1982188-3-paulmck@kernel.org> (raw)
In-Reply-To: <7f398d4a-7fae-4382-9cc4-8627e8aa912b@paulmck-laptop>

From: Bradley Morgan <brads@mainlining.org>

ARC has no two-byte atomic compare and swap, so the
arch_cmpxchg_relaxed() macro switch lets case 2 fall through to
BUILD_BUG() via default, and a two-byte cmpxchg() fails the build.

Route case 2 through the new cmpxchg_emu_u16(), which narrows the
old and new values itself, so the dispatch keeps the (uintptr_t)
casts the case 1 path already uses.

The sizeof(*(_p_)) fix that v4 folded in here landed separately
through Vineet's f050c3e61d2a, so this patch is now only the
case 2 wiring.

Signed-off-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 arch/arc/include/asm/cmpxchg.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index 76f43db0890fc..7157718f147c1 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -50,6 +50,9 @@
 	case 1:								\
 		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
 		break;							\
+	case 2:								\
+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
+		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
 		break;							\
-- 
2.40.1


WARNING: multiple messages have this Message-ID (diff)
From: "Paul E. McKenney" <paulmck@kernel.org>
To: linux-kernel@vger.kernel.org
Cc: Bradley Morgan <brads@mainlining.org>,
	Vineet Gupta <vgupta@kernel.org>, Guo Ren <guoren@kernel.org>,
	Yoshinori Sato <ysato@users.sourceforge.jp>,
	Rich Felker <dalias@libc.org>,
	John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>,
	Chris Zankel <chris@zankel.net>,
	Max Filippov <jcmvbkbc@gmail.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Arnd Bergmann <arnd@kernel.org>,
	David Laight <david.laight.linux@gmail.com>,
	linux-snps-arc@lists.infradead.org, linux-csky@vger.kernel.org,
	linux-sh@vger.kernel.org, kernel-team@meta.com,
	"Paul E . McKenney" <paulmck@kernel.org>
Subject: [PATCH 3/5] ARC: Emulate two-byte cmpxchg
Date: Wed,  7 Oct 2026 13:36:34 -0700	[thread overview]
Message-ID: <20261007203636.1982188-3-paulmck@kernel.org> (raw)
In-Reply-To: <7f398d4a-7fae-4382-9cc4-8627e8aa912b@paulmck-laptop>

From: Bradley Morgan <brads@mainlining.org>

ARC has no two-byte atomic compare and swap, so the
arch_cmpxchg_relaxed() macro switch lets case 2 fall through to
BUILD_BUG() via default, and a two-byte cmpxchg() fails the build.

Route case 2 through the new cmpxchg_emu_u16(), which narrows the
old and new values itself, so the dispatch keeps the (uintptr_t)
casts the case 1 path already uses.

The sizeof(*(_p_)) fix that v4 folded in here landed separately
through Vineet's f050c3e61d2a, so this patch is now only the
case 2 wiring.

Signed-off-by: Bradley Morgan <brads@mainlining.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
---
 arch/arc/include/asm/cmpxchg.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arc/include/asm/cmpxchg.h b/arch/arc/include/asm/cmpxchg.h
index 76f43db0890fc..7157718f147c1 100644
--- a/arch/arc/include/asm/cmpxchg.h
+++ b/arch/arc/include/asm/cmpxchg.h
@@ -50,6 +50,9 @@
 	case 1:								\
 		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u8((volatile u8 *__force)_p_, (uintptr_t)_o_, (uintptr_t)_n_);	\
 		break;							\
+	case 2:								\
+		_prev_ = (__typeof__(*(ptr)))cmpxchg_emu_u16((volatile u16 *__force)_p_, (unsigned long)_o_, (unsigned long)_n_);	\
+		break;							\
 	case 4:								\
 		_prev_ = __cmpxchg(_p_, _o_, _n_);			\
 		break;							\
-- 
2.40.1


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  parent reply	other threads:[~2026-10-07 20:36 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-07 20:36 [PATCH 0/5] Provide two-byte cmpxchg() emulation Paul E. McKenney
2026-10-07 20:36 ` Paul E. McKenney
2026-10-07 20:36 ` [PATCH 1/5] lib: Add two-byte cmpxchg emulation function Paul E. McKenney
2026-10-07 20:36   ` Paul E. McKenney
2026-10-07 20:36 ` [PATCH 2/5] sh: Emulate two-byte cmpxchg Paul E. McKenney
2026-10-07 20:36   ` Paul E. McKenney
2026-10-07 20:36 ` Paul E. McKenney [this message]
2026-10-07 20:36   ` [PATCH 3/5] ARC: " Paul E. McKenney
2026-10-07 20:48   ` Vineet Gupta
2026-10-07 20:48     ` Vineet Gupta
2026-10-07 20:58     ` Paul E. McKenney
2026-10-07 20:58       ` Paul E. McKenney
2026-10-07 20:36 ` [PATCH 4/5] csky: " Paul E. McKenney
2026-10-07 20:36   ` Paul E. McKenney
2026-10-08  5:54   ` Guo Ren
2026-10-08  5:54     ` Guo Ren
2026-10-08 15:38     ` Paul E. McKenney
2026-10-08 15:38       ` Paul E. McKenney
2026-10-07 20:36 ` [PATCH 5/5] xtensa: " Paul E. McKenney
2026-10-07 20:36   ` Paul E. McKenney

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