From 6246541522845a443b7ae4a8f0e16facc5a91198 Mon Sep 17 00:00:00 2001 From: Matt Evans Date: Wed, 1 Feb 2023 18:39:48 +0000 Subject: [PATCH] locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value __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 Signed-off-by: Arnd Bergmann --- 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;