linux-kernel - [PATCH] io: prevent compiler reordering on the default writeX() implementation

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Date:   Fri, 30 Mar 2018 10:29:58 -0400
From:   Sinan Kaya <okaya@...eaurora.org>
To:     arnd@...db.de, timur@...eaurora.org, sulrich@...eaurora.org
Cc:     linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Sinan Kaya <okaya@...eaurora.org>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH] io: prevent compiler reordering on the default writeX() implementation

The default implementation of mapping writeX() to __raw_writeX() is wrong.
writeX() has stronger ordering semantics. Compiler is allowed to reorder
__raw_writeX().

In the abscence of a write barrier or when using a strongly ordered
architecture, writeX() should at least have a compiler barrier in
it to prevent commpiler from clobbering the execution order.

Signed-off-by: Sinan Kaya <okaya@...eaurora.org>
---
 include/asm-generic/io.h | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
index b4531e3..fbbf2bb 100644
--- a/include/asm-generic/io.h
+++ b/include/asm-generic/io.h
@@ -153,6 +153,7 @@ static inline void writeb(u8 value, volatile void __iomem *addr)
 static inline void writew(u16 value, volatile void __iomem *addr)
 {
 	__raw_writew(cpu_to_le16(value), addr);
+	barrier();
 }
 #endif
 
@@ -161,6 +162,7 @@ static inline void writew(u16 value, volatile void __iomem *addr)
 static inline void writel(u32 value, volatile void __iomem *addr)
 {
 	__raw_writel(__cpu_to_le32(value), addr);
+	barrier();
 }
 #endif
 
@@ -170,6 +172,7 @@ static inline void writel(u32 value, volatile void __iomem *addr)
 static inline void writeq(u64 value, volatile void __iomem *addr)
 {
 	__raw_writeq(__cpu_to_le64(value), addr);
+	barrier();
 }
 #endif
 #endif /* CONFIG_64BIT */
-- 
2.7.4