Re: [PATCH 4/5] context_tracking: Only define schedule_user() on !HAVE_CONTEXT_TRACKING_OFFSTACK archs

[Peter Zijlstra]

On Tue, Oct 27, 2020 at 04:08:26PM +0100, Frederic Weisbecker wrote:
> schedule_user() was traditionally used by the entry code's tail to
> preempt userspace after the call to user_enter(). Indeed the call to
> user_enter() used to be performed upon syscall exit slow path which was
> right before the last opportunity to schedule() while resuming to
> userspace. The context tracking state had to be saved on the task stack
> and set back to CONTEXT_KERNEL temporarily in order to safely switch to
> another task.
> 
> Only a few archs use it now and those implementing
> HAVE_CONTEXT_TRACKING_OFFSTACK definetly can't rely on it.

powerpc64 and sparc64 only, right?

> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Phil Auld <pauld@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> ---
>  kernel/sched/core.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index c23d7cb5aee3..44426e5acde2 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4631,7 +4631,7 @@ void __sched schedule_idle(void)
>  	} while (need_resched());
>  }
>  
> -#ifdef CONFIG_CONTEXT_TRACKING
> +#if defined(CONFIG_CONTEXT_TRACKING) && !defined(CONFIG_HAVE_CONTEXT_TRACKING_OFFSTACK)
>  asmlinkage __visible void __sched schedule_user(void)
>  {
>  	/*
> -- 
> 2.25.1
>