On Tue, Aug 04, 2020 at 10:59:33AM -0400, Mathieu Desnoyers wrote:
> ----- On Aug 4, 2020, at 10:51 AM, Peter Zijlstra [email protected] wrote:
> > On Tue, Jul 28, 2020 at 12:00:10PM -0400, Mathieu Desnoyers wrote:
> >> task_lock(tsk);
> >> + /*
> >> + * When a kthread stops operating on an address space, the loop
> >> + * in membarrier_{private,global}_expedited() may not observe
> >> + * that tsk->mm, and not issue an IPI. Membarrier requires a
> >> + * memory barrier after accessing user-space memory, before
> >> + * clearing tsk->mm.
> >> + */
> >> + smp_mb();
> >> sync_mm_rss(mm);
> >> local_irq_disable();
> >
> > Would it make sense to put the smp_mb() inside the IRQ disable region?
>
> I've initially placed it right after task_lock so we could eventually
> have a smp_mb__after_non_raw_spinlock or something with a much better naming,
> which would allow removing the extra barrier when it is implied by the
> spinlock.
Oh, right, fair enough. I'll go think about if smp_mb__after_spinlock()
will work for mutexes too.
It basically needs to upgrade atomic*_acquire() to smp_mb(). So that's
all architectures that have their own _acquire() and an actual
smp_mb__after_atomic().
Which, from the top of my head are only arm64, power and possibly riscv.
And if I then git-grep smp_mb__after_spinlock, all those seem to be
covered.
But let me do a better audit..
