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 <frede...@kernel.org>
> Cc: Marcelo Tosatti <mtosa...@redhat.com>
> Cc: Paul E. McKenney <paul...@kernel.org>
> Cc: Peter Zijlstra <pet...@infradead.org>
> Cc: Phil Auld <pa...@redhat.com>
> Cc: Thomas Gleixner <t...@linutronix.de>
> ---
> 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
>
