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SubjectRe: [PATCH 08/11] membarrier: Provide core serializing command (v2)
On Tue, Jan 23, 2018 at 10:57:30AM -0500, Mathieu Desnoyers wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index f38c4c7e256a..041893128f51 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2662,9 +2662,13 @@ static struct rq *finish_task_switch(struct task_struct *prev)
> * thread, mmdrop()'s implicit full barrier is required by the
> * membarrier system call, because the current active_mm can
> * become the current mm without going through switch_mm().
> + * membarrier also requires a core serializing instruction
> + * before going back to user-space after storing to rq->curr.
> */
> - if (mm)
> + if (mm) {
> + membarrier_mm_sync_core_before_usermode(mm);
> mmdrop(mm);
> + }

*confused*, when we switch from process A to process B, context_switch()
will not set rq->prev_mm and the above mm will be NULL and we'll not
pass through your_function_names_are_waaay_too_long and we'll not get
cookies.

And if there's anything more complicated going on, the comment/changelog
are not adequate.

> if (unlikely(prev_state == TASK_DEAD)) {
> if (prev->sched_class->task_dead)
> prev->sched_class->task_dead(prev);


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