On Thu, Jul 20, 2023 at 10:00 PM Alan Huang <mmpgouride@xxxxxxxxx> wrote: > > > > 2023年7月21日 03:22，Eric Dumazet <edumazet@xxxxxxxxxx> 写道： > > > > On Thu, Jul 20, 2023 at 8:54 PM Alan Huang <mmpgouride@xxxxxxxxx> wrote: > >> > >> Hi, > >> > >> I noticed a commit c87a124a5d5e(“net: force a reload of first item in hlist_nulls_for_each_entry_rcu”) > >> and a related discussion [1]. > >> > >> After reading the whole discussion, it seems like that ptr->field was cached by gcc even with the deprecated > >> ACCESS_ONCE(), so my question is: > >> > >> Is that a compiler bug? If so, has this bug been fixed today, ten years later? > >> > >> What about READ_ONCE(ptr->field)? > > > > Make sure sparse is happy. > > It caused a problem without barrier(), and the deprecated ACCESS_ONCE() didn’t help: > > https://lore.kernel.org/all/519D19DA.50400@xxxxxxxxxxxxxx/ > > So, my real question is: With READ_ONCE(ptr->field), are there still some unusual cases where gcc > decides not to reload ptr->field? I can not really answer without seeing an actual patch... Why are you asking ? Are you tracking compiler bug fixes ? > > > > > Do you have a patch for review ? > > Possibly next month. :) > > > > > > >> > >> > >> [1] https://lore.kernel.org/all/1369699930.3301.494.camel@edumazet-glaptop/ > >> > >> Thanks, > >> Alan >
