On Fri, Feb 15, 2019 at 01:10:33AM +0200, Igor Stoppa wrote:
>
>
> On 14/02/2019 13:28, Peter Zijlstra wrote:
> > On Thu, Feb 14, 2019 at 12:41:32AM +0200, Igor Stoppa wrote:
>
> [...]
>
> > > +#define wr_rcu_assign_pointer(p, v) ({ \
> > > + smp_mb(); \
> > > + wr_assign(p, v); \
> > > + p; \
> > > +})
> >
> > This requires that wr_memcpy() (through wr_assign) is single-copy-atomic
> > for native types. There is not a comment in sight that states this.
>
> Right, I kinda expected native-aligned <-> atomic, but it's not necessarily
> true. It should be confirmed when enabling write rare on a new architecture.
> I'll add the comment.
>
> > Also, is this true of x86/arm64 memcpy ?
>
>
> For x86_64:
> https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/x86/include/asm/uaccess.h#L462
> the mov"itype" part should deal with atomic copy of native, aligned types.
>
>
> For arm64:
> https://elixir.bootlin.com/linux/v5.0-rc6/source/arch/arm64/lib/copy_template.S#L110
> .Ltiny15 deals with copying less than 16 bytes, which includes pointers.
> When the data is aligned, the copy of a pointer should be atomic.
>
Where are the comments and Changelog notes ? How is an arch maintainer
to be aware of this requirement when adding support for his/her arch?
