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SubjectRe: [PATCH v2] sched: Make const-safe
On Wed, Dec 14, 2022 at 06:03:04PM +0000, Matthew Wilcox wrote:
> On Wed, Dec 14, 2022 at 10:11:01AM +0100, Peter Zijlstra wrote:
> > On Mon, Dec 12, 2022 at 02:49:46PM +0000, Matthew Wilcox (Oracle) wrote:
> > > With a modified container_of() that preserves constness, the compiler
> > > finds some pointers which should have been marked as const. task_of()
> > > also needs to become const-preserving for the !FAIR_GROUP_SCHED case so
> > > that cfs_rq_of() can take a const argument. No change to generated code.
> >
> > More const more better I suppose.. Thanks!
> >
> > Happen to have a sha for the container_of() commit handy?
>
> There isn't one yet. Obviously we can't make container_of()
> const-preserving until we've fixed all the places which would warn.
> The diff I have in my tree looks like this:
>
> diff --git a/include/linux/container_of.h b/include/linux/container_of.h
> index 1d898f9158b4..9416e6cc8c88 100644
> --- a/include/linux/container_of.h
> +++ b/include/linux/container_of.h
> @@ -20,7 +20,10 @@
> static_assert(__same_type(*(ptr), ((type *)0)->member) || \
> __same_type(*(ptr), void), \
> "pointer type mismatch in container_of()"); \
> - ((type *)(__mptr - offsetof(type, member))); })
> + __mptr -= offsetof(type, member); \
> + _Generic(ptr, \
> + const typeof(*(ptr)) *: (const type *)__mptr, \
> + default: ((type *)__mptr)); })

Ah nice. Thanks!

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