Unverified Commit 62465415 authored by Matt Evans's avatar Matt Evans Committed by Arnd Bergmann
Browse files

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: default avatarMatt Evans <mev@rivosinc.com>
Signed-off-by: default avatarArnd Bergmann <arnd@arndb.de>
parent 88603b6d

include/asm-generic/cmpxchg-local.h

+3 −3
Original line number Diff line number Diff line
@@ -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;