linux-kernel - [PATCH 2/3] percpu: Introduce PERCPU

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Message-ID: <20241021080856.48746-2-ubizjak@gmail.com>
Date: Mon, 21 Oct 2024 10:07:37 +0200
From: Uros Bizjak <ubizjak@...il.com>
To: linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Cc: Uros Bizjak <ubizjak@...il.com>,
	Dennis Zhou <dennis@...nel.org>,
	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: [PATCH 2/3] percpu: Introduce PERCPU_PTR() macro

Introduce PERCPU_PTR() macro to cast the percpu pointer from
the percpu address space to a generic (kernel) address space.
Use it in per_cpu_ptr() and related SHIFT_PERCPU_PTR() macros.

Also remove common knowledge from SHIFT_PERCPU_PTR() comment,
"weird cast" is just a standard way to inform sparse of a cast
from the percpu address space to a generic address space.

Signed-off-by: Uros Bizjak <ubizjak@...il.com>
Cc: Dennis Zhou <dennis@...nel.org>
Cc: Tejun Heo <tj@...nel.org>
Cc: Christoph Lameter <cl@...ux.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>
---
 include/linux/percpu-defs.h | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/percpu-defs.h b/include/linux/percpu-defs.h
index 7fa88c5f4b26..e1cf7982424f 100644
--- a/include/linux/percpu-defs.h
+++ b/include/linux/percpu-defs.h
@@ -220,15 +220,17 @@ do {									\
 	(void)__vpp_verify;						\
 } while (0)
 
+#define PERCPU_PTR(__p)							\
+	(typeof(*(__p)) __force __kernel *)(__p);
+
 #ifdef CONFIG_SMP
 
 /*
- * Add an offset to a pointer but keep the pointer as-is.  Use RELOC_HIDE()
- * to prevent the compiler from making incorrect assumptions about the
- * pointer value.  The weird cast keeps both GCC and sparse happy.
+ * Add an offset to a pointer.  Use RELOC_HIDE() to prevent the compiler
+ * from making incorrect assumptions about the pointer value.
  */
 #define SHIFT_PERCPU_PTR(__p, __offset)					\
-	RELOC_HIDE((typeof(*(__p)) __kernel __force *)(__p), (__offset))
+	RELOC_HIDE(PERCPU_PTR(__p), (__offset))
 
 #define per_cpu_ptr(ptr, cpu)						\
 ({									\
@@ -258,7 +260,7 @@ do {									\
 ({									\
 	(void)(cpu);							\
 	__verify_pcpu_ptr(ptr);						\
-	(typeof(*(ptr)) __kernel __force *)(ptr);			\
+	PERCPU_PTR(ptr);						\
 })
 
 #define raw_cpu_ptr(ptr)	per_cpu_ptr(ptr, 0)
-- 
2.47.0