Re: [PATCH] locking/atomic: cmpxchg: Make __generic_cmpxchg_local compare against zero-extended 'old' value

[Arnd Bergmann]

On Wed, Feb 1, 2023, at 19:39, Matt Evans wrote:
> __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>
> ---

Applied to the asm-generic tree for 6.3, thanks

    Arnd