> On Feb 6, 2020, at 4:04 AM, Jan Kara <jack@xxxxxxx> wrote: > > So in this particular case, store tearing is non-issue because we use > atomic operation to store the value in page_cpupid_xchg_last(). I think it > would make some sense to use READ_ONCE(page->flags) here to prevent > compiler from loading page->flags several times - I have hard time finding > a reason why a compiler would want to do that but conceptually that > protection makes sense, it is for free performance wise, and will still > allow KCSAN to find a race in case we ever grow a place that modifies > page's zone non-atomically (which might be a real problem). And it should > also silence the KCSAN warning AFAIU. Ah, read up to 3 bits might be an issue then. I’ll post an alternative version which uses READ_ONCE() just for the old page ( because the new page has not been published yet) in wp_page_copy() then.
