linux-kernel - [50/91] sparc64: Fix rwsem constant bug leading to hangs.

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Message-Id: <20100824224216.354425785@clark.site>
Date:	Tue, 24 Aug 2010 15:42:12 -0700
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	"David S. Miller" <davem@...emloft.net>
Subject: [50/91] sparc64: Fix rwsem constant bug leading to hangs.

2.6.34-stable review patch.  If anyone has any objections, please let us know.

------------------

From: David S. Miller <davem@...emloft.net>

[ Upstream commit ef201bebe5afc91a2b99b45dacc8c6dd88ca9e58 ]

As noticed by Linus, it is critical that some of the
rwsem constants be signed.  Yet, hex constants are
unsigned unless explicitly casted or negated.

The most critical one is RWSEM_WAITING_BIAS.

This bug was exacerbated by commit
424acaaeb3a3932d64a9b4bd59df6cf72c22d8f3 ("rwsem: wake queued readers
when writer blocks on active read lock")

Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>
---
 arch/sparc/include/asm/rwsem-const.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/sparc/include/asm/rwsem-const.h
+++ b/arch/sparc/include/asm/rwsem-const.h
@@ -5,7 +5,7 @@
 #define RWSEM_UNLOCKED_VALUE		0x00000000
 #define RWSEM_ACTIVE_BIAS		0x00000001
 #define RWSEM_ACTIVE_MASK		0x0000ffff
-#define RWSEM_WAITING_BIAS		0xffff0000
+#define RWSEM_WAITING_BIAS		(-0x00010000)
 #define RWSEM_ACTIVE_READ_BIAS		RWSEM_ACTIVE_BIAS
 #define RWSEM_ACTIVE_WRITE_BIAS		(RWSEM_WAITING_BIAS + RWSEM_ACTIVE_BIAS)
 


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