On Tue, Jul 9, 2024, at 15:45, Geert Uytterhoeven wrote: > On Tue, Jul 9, 2024 at 1:58 PM Jeff Layton <jlayton@xxxxxxxxxx> wrote: >> I've been getting some of these warning emails from the KTR. I think >> this is in reference to this patch, which adds a 64-bit try_cmpxchg in >> the timestamp handling code: >> >> https://lore.kernel.org/linux-fsdevel/20240708-mgtime-v4-0-a0f3c6fb57f3@xxxxxxxxxx/ >> >> On m68k, there is a prototype for __invalid_cmpxchg_size, but no actual >> function, AFAICT. Should that be defined somewhere, or is this a >> deliberate way to force a build break in this case? > > It's a deliberate way to break the build. > >> More to the point though: do I need to do anything special for m86k >> here (or for other arches that can't do a native 64-bit cmpxchg)? > > 64-bit cmpxchg() is only guaranteed to exist on 64-bit platforms. > See also > https://elixir.bootlin.com/linux/latest/source/include/asm-generic/cmpxchg.h#L62 > > I think you can use arch_cmpxchg64(), though. arch_cmpxchg64() is an internal helper provided by some architectures. Driver code should use cmpxchg64() for the explicitly 64-bit sized atomic operation. I'm fairly sure we still don't provide this across all 32-bit architectures though: on architectures that have 64-bit atomics (i686, armv6k, ...) these can be provided architecture specific code, and on non-SMP kernels they can use the generic fallback through generic_cmpxchg64_local(), but on SMP architectures without native atomics you need a Kconfig dependency to turn off the particular code. Arnd
