linux-kernel - [PATCH] riscv/atomic: Do proper sign extension also for unsigned in arch

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Message-ID: <mvmed0k4prh.fsf@suse.de>
Date: Thu, 30 Jan 2025 10:25:38 +0100
From: Andreas Schwab <schwab@...e.de>
To: linux-riscv@...ts.infradead.org
CC: linux-kernel@...r.kernel.org
Subject: [PATCH] riscv/atomic: Do proper sign extension also for unsigned in
 arch_cmpxchg

Sign extend also an unsigned compare value to match what lr.w is doing.
Otherwise try_cmpxchg may spuriously return true when used on a u32 value
that has the sign bit set, as it happens often in inode_set_ctime_current.

Do this in three conversion steps.  The first conversion to long is needed
to avoid a -Wpointer-to-int-cast warning when arch_cmpxchg is used with a
pointer type.  Then convert to int and back to long to always sign extend
the 32-bit value to 64-bit.

Fixes: 6c58f25e6938 ("riscv/atomic: Fix sign extension for RV64I")
Signed-off-by: Andreas Schwab <schwab@...e.de>
---
 arch/riscv/include/asm/cmpxchg.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 4cadc56220fe..427c41dde643 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -231,7 +231,7 @@
 		__arch_cmpxchg(".w", ".w" sc_sfx, ".w" cas_sfx,		\
 			       sc_prepend, sc_append,			\
 			       cas_prepend, cas_append,			\
-			       __ret, __ptr, (long), __old, __new);	\
+			       __ret, __ptr, (long)(int)(long), __old, __new);	\
 		break;							\
 	case 8:								\
 		__arch_cmpxchg(".d", ".d" sc_sfx, ".d" cas_sfx,		\
-- 
2.48.1


-- 
Andreas Schwab, SUSE Labs, schwab@...e.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE  1748 E4D4 88E3 0EEA B9D7
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