Messages in this thread | | | Date | Fri, 23 Jul 2021 12:59:47 -0400 | From | Alan Stern <> | Subject | Re: [PATCH memory-model 2/4] tools/memory-model: Add example for heuristic lockless reads |
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On Fri, Jul 23, 2021 at 09:24:31AM -0700, Paul E. McKenney wrote: > On Thu, Jul 22, 2021 at 10:08:46PM -0400, Alan Stern wrote:
> > > + void do_something_locked(struct foo *fp) > > > + { > > > + bool gf = true; > > > + > > > + /* IMPORTANT: Heuristic plus spin_lock()! */ > > > + if (!data_race(global_flag)) { > > > + spin_lock(&fp->f_lock); > > > + if (!smp_load_acquire(&global_flag)) {
> > > + void begin_global(void) > > > + { > > > + int i; > > > + > > > + spin_lock(&global_lock); > > > + WRITE_ONCE(global_flag, true); > > > > Why does this need to be WRITE_ONCE? It still races with the first read > > of global_flag above. > > But also with the smp_load_acquire() of global_flag, right?
What I'm curious about is why, given these two races, you notate one of them by changing a normal write to WRITE_ONCE and you notate the other by changing a normal read to a data_race() read. Why not handle them both the same way?
Alan
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