__generic_cmpxchg_local takes unsigned long old/new arguments which
might end up being up-cast from smaller signed types (which will
sign-extend). The loaded compare value must be compared against a
truncated smaller type, so down-cast appropriately for each size.
The issue is apparent on 64-bit machines with code, such as
atomic_dec_unless_positive(), that sign-extends from int.
64-bit machines generally don't use the generic cmpxchg but
development/early ports might make use of it, so make it correct.
Signed-off-by: Matt Evans <mev@xxxxxxxxxxxx>
---
include/asm-generic/cmpxchg-local.h | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/include/asm-generic/cmpxchg-local.h b/include/asm-generic/cmpxchg-local.h
index 380cdc824e4b..c3e7315b7c1d 100644
--- a/include/asm-generic/cmpxchg-local.h
+++ b/include/asm-generic/cmpxchg-local.h
@@ -26,15 +26,15 @@ static inline unsigned long __generic_cmpxchg_local(volatile void *ptr,
raw_local_irq_save(flags);
switch (size) {
case 1: prev = *(u8 *)ptr;
- if (prev == old)
+ if (prev == (u8)old)
*(u8 *)ptr = (u8)new;
break;
case 2: prev = *(u16 *)ptr;
- if (prev == old)
+ if (prev == (u16)old)
*(u16 *)ptr = (u16)new;
break;
case 4: prev = *(u32 *)ptr;
- if (prev == old)
+ if (prev == (u32)old)
*(u32 *)ptr = (u32)new;
break;
case 8: prev = *(u64 *)ptr;
--
2.30.2
