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

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On Thu, Oct 13, 2016 at 4:41 PM, Mark Rutland <mark.rutland@arm.com> wrote:
> Hi,
>
> On Thu, Oct 13, 2016 at 01:57:10PM +0200, Heiko Carstens wrote:
>> 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.
>
> The exact same applies for arm64 on all counts. This is also simpler than both
> attempts I had at this, so FWIW:
>
> Acked-by: Mark Rutland <mark.rutland@arm.com>
>
> To make merging less painful, I guess we'll need a stable branch with (just)
> this and whatever patch we end up with for fixing current_thread_info(), so we
> can independently merge the arch-specific parts.
>
> I guess it'd make sense for the tip tree to host that?
>

I wonder if this could even make 4.9.  It's pretty clearly a no-op.  Ingo?

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[PATCH 0/3] THREAD_INFO_IN_TASK_STRUCT vs generic preemption code Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-13 14:50 +0200
  [PATCH 1/3] sched/core,x86: make struct thread_info arch specific again Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-13 15:10 +0200
    Re: [PATCH 1/3] sched/core,x86: make struct thread_info arch  specific again Mark Rutland <mark.rutland@arm.com> - 2016-10-14 01:50 +0200
      Re: [PATCH 1/3] sched/core,x86: make struct thread_info arch specific again Andy Lutomirski <luto@amacapital.net> - 2016-10-14 02:00 +0200
  [PATCH 2/3] sched/preempt: include asm/current.h Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-13 15:10 +0200
    Re: [PATCH 2/3] sched/preempt: include asm/current.h Mark Rutland <mark.rutland@arm.com> - 2016-10-14 01:30 +0200
      Re: [PATCH 2/3] sched/preempt: include asm/current.h Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-14 10:20 +0200
        [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK (WAS: [PATCH 2/3] sched/preempt: include asm/current.h) Mark Rutland <mark.rutland@arm.com> - 2016-10-14 12:50 +0200
          Re: [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK  (WAS: [PATCH 2/3] sched/preempt: include asm/current.h) Mark Rutland <mark.rutland@arm.com> - 2016-10-17 16:50 +0200
            Re: [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK  (WAS: [PATCH 2/3] sched/preempt: include asm/current.h) Mark Rutland <mark.rutland@arm.com> - 2016-10-17 19:40 +0200
              Re: [PATCH] thread_info: include <current.h> for THREAD_INFO_IN_TASK  (WAS: [PATCH 2/3] sched/preempt: include asm/current.h) Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-18 12:40 +0200
  [PATCH 3/3] s390: move thread_info into task_struct Heiko Carstens <heiko.carstens@de.ibm.com> - 2016-10-13 22:10 +0200
  Re: [PATCH 0/3] THREAD_INFO_IN_TASK_STRUCT vs generic preemption code Andy Lutomirski <luto@amacapital.net> - 2016-10-14 00:10 +0200

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