On Fri, May 14, 2021 at 12:02:05PM +0800, Huang, Ying wrote: > Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> writes: > > 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? > > In addition to p->type, *p is zeroed via kvzalloc(). So it is, good point. > > 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. > > We usually check the state of swap_info_struct before other operations. > For example, we check si->swap_map in swap_start(). Yes, we usually do. > > 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? > > I think we have initialized all fields before publication :-). Probably all the ones that matter in practice, yes :-) Still feeling slightly uneasy about the theoretical p->lock, but that was possible before this change too so it's out of scope. A comment explaining the pairing and that we care mostly about the zero init would be nice.
