Re: [PATCH 1/3] sched/core,x86: make struct thread_info arch specific again

[Ingo Molnar <mingo@kernel.org>]

* Andy Lutomirski <luto@amacapital.net> wrote:

> On Wed, Oct 19, 2016 at 11:28 AM, Mark Rutland <mark.rutland@arm.com> wrote:
> > From: Heiko Carstens <heiko.carstens@de.ibm.com>
> >
> > commit c65eacbe290b ("sched/core: Allow putting thread_info into
> > task_struct") made struct thread_info a generic struct with only a
> > single flags member if THREAD_INFO_IN_TASK_STRUCT is selected.
> >
> > This change however seems to be quite x86 centric, since at least the
> > generic preemption code (asm-generic/preempt.h) assumes that struct
> > thread_info also has a preempt_count member, which apparently was not
> > true for x86.
> >
> > We could add a bit more ifdefs to solve this problem too, but it seems
> > to be much simpler to make struct thread_info arch specific
> > again. This also makes the conversion to THREAD_INFO_IN_TASK_STRUCT a
> > bit easier for architectures that have a couple of arch specific stuff
> > in their thread_info definition.
> >
> > The arch specific stuff _could_ be moved to thread_struct. However
> > keeping them in thread_info makes it easier: accessing thread_info
> > members is simple, since it is at the beginning of the task_struct,
> > while the thread_struct is at the end. At least on s390 the offsets
> > needed to access members of the thread_struct (with task_struct as
> > base) are too large for various asm instructions.  This is not a
> > problem when keeping these members within thread_info.
> 
> Acked-by: Andy Lutomirski <luto@kernel.org>
> 
> Ingo, there's a (somewhat weak) argument for sending this via
> tip/urgent: it doesn't change generated code at all, and I think it
> will avoid a silly depedency or possible conflict for the next merge
> window, since both arm64 and s390 are going to need it.

Can certainly do it if this is the final version of the patch. Mark?

Thanks,

	Ingo