On Fri, Aug 11, 2017 at 07:39:17AM -0700, Paul E. McKenney wrote: > On Fri, Aug 11, 2017 at 11:14:34AM +0200, Peter Zijlstra wrote: > > On Thu, Aug 10, 2017 at 09:54:53PM -0700, Paul E. McKenney wrote: > > > On Fri, Aug 11, 2017 at 02:43:52PM +1000, Stephen Rothwell wrote: > > > > > > Looks like I need to rebase my patch on top of a9668cd6ee28, and > > > than put an smp_mb__after_spinlock() between the lock and the unlock. > > > > > > Peter, any objections to that approach? Other suggestions? > > > > Hurm.. I'll have to try and understand that comment there again it > > seems. > > My reasoning is as follows: > > 1. The critical section is empty, so any prior references > would be ordered only against later critical sections. > > 2. A full barrier within the critical section will order those > prior references against later critical sections just > as easily as would one prior to the critical section. > > Does that make sense, I should I have stayed away from the keyboard > at this early hour? ;-) So I think we can do away with 2 because our prior and later stores have an address dependency (they are to the same variable) and thus must be ordered already. Basically: CPU0 CPU1 p->state = TASK_UNINTERRUPTIBLE; try_to_wake_up(p) p->state = TASK_RUNNING spin_lock(&p->pi_lock); spin_unlock(&p->pi_lock); p->state = TASK_DEAD Now, the ttwu(p) NO-OPs unless it sees (UN)INTERRUPTIBLE, so either RUNNING or DEAD are fine. However if it sees (UN)INTERRUPTIBLE it will do another (competing) RUNNING store which must not overwrite DEAD. -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
