Re: [PATCH 5/6] sh: Emulate two-byte cmpxchg

[Bradley Morgan]

On 16 September 2026 22:01:07 BST, "Paul E. McKenney" <paulmck@xxxxxxxxxx>
wrote:
>On Wed, Sep 16, 2026 at 09:16:16PM +0200, John Paul Adrian Glaubitz wrote:
>> Hi Bradley,
>> 
>> On Fri, 2026-09-11 at 19:25 +0000, Bradley Morgan wrote:
>> > SH has no byte or halfword atomic memory operations, so the
>> > __cmpxchg() switch routes case 1 through cmpxchg_emu_u8() and
>> > lets case 2 fall through to __cmpxchg_called_with_bad_pointer(),
>> > which is declared but never defined, so a two-byte cmpxchg()
>> > fails at link time. Route case 2 through the new cmpxchg_emu_u16().
>> > 
>> > Signed-off-by: Bradley Morgan <brads@xxxxxxxxxxxxxx>
>> > ---
>> >  arch/sh/include/asm/cmpxchg.h | 2 ++
>> >  1 file changed, 2 insertions(+)
>> > 
>> > diff --git a/arch/sh/include/asm/cmpxchg.h
>b/arch/sh/include/asm/cmpxchg.h
>> > index 1e5dc5ccf7bf..477d3025a441 100644
>> > --- a/arch/sh/include/asm/cmpxchg.h
>> > +++ b/arch/sh/include/asm/cmpxchg.h
>> > @@ -59,6 +59,8 @@ static inline unsigned long __cmpxchg(volatile void
>* ptr, unsigned long old,
>> >  	switch (size) {
>> >  	case 1:
>> >  		return cmpxchg_emu_u8(ptr, old, new);
>> > +	case 2:
>> > +		return cmpxchg_emu_u16(ptr, old, new);
>> >  	case 4:
>> >  		return __cmpxchg_u32(ptr, old, new);
>> >  	}
>> 
>> Odd, I thought this series was merged long time ago. Was there anything
>holding it back?
>
>You might be thinking of the cmpxchg_emu_u8() series from a few years
>back.
>This is cmpxchg_emu_u16().
>
>							Thanx, Paul
>
>> Either way:
>> 
>> Acked-by: John Paul Adrian Glaubitz <glaubitz@xxxxxxxxxxxxxxxxxxx>
>> 
>> Adrian
>> 
>> -- 
>>  .''`.  John Paul Adrian Glaubitz
>> : :' :  Debian Developer
>> `. `'   Physicist
>>   `-    GPG: 62FF 8A75 84E0 2956 9546  0006 7426 3B37 F5B5 F913
I think he was referring to when you tried u16 that time.
--- Thanks!
https://lore.kernel.org/all/EE579805-42F2-4C58-B752-F28779EEB717@xxxxxxxxx/