----- On Aug 5, 2020, at 6:59 AM, Peter Zijlstra [email protected] wrote:
> 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() ? As discussed over IRC, smp_mb__after_atomic_acquire() would be better, because load_acquire and spin_lock have different semantic. We could keep a define of smp_mb__after_spinlock to smp_mb__after_atomic_acquire to make the transition simpler. Thanks, Mathieu -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
