[PATCH] riscv/atomic: Do proper sign extension also for unsigned in arch_cmpxchg

Andreas Schwab
2025-01-30T09:25:40Z

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@suse.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@suse.de
GPG Key fingerprint = 0196 BAD8 1CE9 1970 F4BE 1748 E4D4 88E3 0EEA B9D7
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