On Mon, Jul 22, 2019 at 06:34:22PM +0000, Nadav Amit wrote: > > On Jul 22, 2019, at 11:21 AM, Peter Zijlstra <pet...@infradead.org> wrote: > > > > On Thu, Jul 18, 2019 at 05:58:29PM -0700, Nadav Amit wrote: > >> +/* > >> + * Call a function on all processors. May be used during early boot while > >> + * early_boot_irqs_disabled is set. > >> + */ > >> +static inline void on_each_cpu(smp_call_func_t func, void *info, int wait) > >> +{ > >> + on_each_cpu_mask(cpu_online_mask, func, info, wait); > >> +} > > > > I'm thinking that one if buggy, nothing protects online mask here. > > on_each_cpu_mask() calls __on_each_cpu_mask() which would disable preemption. > The mask might change, but anyhow __smp_call_function_many() would “and” it, > after disabling preemption, with (the potentially updated) cpu_online_mask.
Ah, indeed, as long as we double check the state after disabling preemption things should be fine. > What is your concern? Pavlov reaction to seeing a naked cpu_online_mask :-)