On Tue, Jul 03, 2018 at 10:59:45AM -0700, Linus Torvalds wrote: > On Tue, Jul 3, 2018 at 10:49 AM Peter Zijlstra <pet...@infradead.org> wrote: > > > > > I can simply document that loads/stores from/to all struct rseq fields > > > should be thread-local then ? > > > > I'm not sure that covers things sufficiently. You really want the > > userspace load/stores to be single instructions. > > Actually, I think we should try very hard to limit even that to _just_ > the rseq pointer itself.
> So I'd suggest that the only part we aim to have any "atomic" behavior > at all is for the individual fields in "struct rseq" itself. So the > cpu id and the base pointer and the flags. And even they are > thread-local, so the atomicity is not about the kernel, but about user > space needing to read and update them in word-sized chunks. > > End result: absolutely nothing is atomic for the kernel. Yes, agreed, that is what I meant but very poorly expressed. Only the rseq bits themselves need this single-copy atomic stuff -- for userspace.
