On Tue, Aug 04, 2020 at 07:01:53PM +0200, [email protected] wrote: > 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..
All I could find is csky, which, afaict, defines a superfluous smp_mb__after_spinlock. The relevant architectures are indeed power, arm64 and riscv, they all have custom acquire/release and all define smp_mb__after_spinlock() appropriately. Should we rename it to smp_mb__after_acquire() ?
