riscv/futex: sign extend compare value in atomic cmpxchg

commit 599c44cd21f4967774e0acf58f734009be4aea9a upstream.

Make sure the compare value in the lr/sc loop is sign extended to match
what lr.w does.  Fortunately, due to the compiler keeping the register
contents sign extended anyway the lack of the explicit extension didn't
result in wrong code so far, but this cannot be relied upon.

Fixes: b90edb3 ("RISC-V: Add futex support.")
Signed-off-by: Andreas Schwab <[email protected]>
Reviewed-by: Alexandre Ghiti <[email protected]>
Reviewed-by: Björn Töpel <[email protected]>
Cc: [email protected]
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

Author: andreas-schwab

arch/riscv/include/asm/futex.h

@@ -93,7 +93,7 @@ futex_atomic_cmpxchg_inatomic(u32 *uval, u32 __user *uaddr,
 		_ASM_EXTABLE_UACCESS_ERR(1b, 3b, %[r])	\
 		_ASM_EXTABLE_UACCESS_ERR(2b, 3b, %[r])	\
 	: [r] "+r" (ret), [v] "=&r" (val), [u] "+m" (*uaddr), [t] "=&r" (tmp)
-	: [ov] "Jr" (oldval), [nv] "Jr" (newval)
+	: [ov] "Jr" ((long)(int)oldval), [nv] "Jr" (newval)
 	: "memory");
 	__disable_user_access();