On Fri, May 14, 2021 at 02:04:14PM +0200, Peter Zijlstra wrote: > On Thu, May 13, 2021 at 09:59:46PM -0400, Daniel Jordan wrote: > > Yes, this does help, I didn't understand why smp_wmb stayed around in > > the original post. > > > > I think the only access smp_store_release() orders is p->type. Wouldn't > > it be kinda inconsistent to only initialize that one field before > > publishing when many others would be done at the end of > > alloc_swap_info() after the fact? p->type doesn't seem special. For > > instance, get_swap_page_of_type() touches si->lock soon after it calls > > swap_type_to_swap_info(), so there could be a small window where there's > > a non-NULL si with an uninitialized lock. > > > > It's not as if this is likely to be a problem in practice, it would just > > make it harder to understand why smp_store_release is there. Maybe all > > we need is a WRITE_ONCE, or if it's really necessary for certain fields > > to be set before publication then move them up and explain? > > You also care about the zero fill from kvzalloc(). Without the > smp_store_release() the zero-fill from the memset() might only be > visible 'late'. Aha, yes, didn't consider that! > Unless that also isn't a problem? No, you're right, we need that for p->flags at least.
