On 29.09.2020 19:18, Julien Grall wrote: > On 29/09/2020 14:37, Jan Beulich wrote: >> On 29.09.2020 15:03, Julien Grall wrote: >>> I am thinking that it may be easier to hold the write lock when doing >>> the update. >> >> ... perhaps this is indeed better. I have to admit that I never >> fully understood the benefit of using spin_barrier() in this code >> (as opposed to the use in evtchn_destroy()). > > I am not entirely sure either. It looks like it is an attempt to make > v->virq_to_evtchn[X] visible without holding a lock. > > Any holder of the lock after spin_barrier() has completed will read 0 > and not try to use the lock.
I'm not sure I follow: A holder of the lock is obviously already making use of the lock. Or are you talking of two different locks here (recall that before XSA-343 there was just one lock involved in sending)? > But the update of v->virq_to_evtchn[X] should have used either > ACCESS_ONCE() or write_atomic(). Of course, like in so many other places in the code base. Jan
