On 22/09/2020 10:23, Arnd Bergmann wrote: > On Tue, Sep 22, 2020 at 8:32 AM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: >> On 22/09/2020 03:58, Andy Lutomirski wrote: >>> On Mon, Sep 21, 2020 at 5:24 PM Pavel Begunkov <asml.silence@xxxxxxxxx> wrote: >>> I may be looking at a different kernel than you, but aren't you >>> preventing creating an io_uring regardless of whether SQPOLL is >>> requested? >> >> I diffed a not-saved file on a sleepy head, thanks for noticing. >> As you said, there should be an SQPOLL check. >> >> ... >> if (ctx->compat && (p->flags & IORING_SETUP_SQPOLL)) >> goto err; > > Wouldn't that mean that now 32-bit containers behave differently > between compat and native execution? > > I think if you want to prevent 32-bit applications from using SQPOLL, > it needs to be done the same way on both to be consistent: The intention was to disable only compat not native 32-bit. > > if ((!IS_ENABLED(CONFIG_64BIT) || ctx->compat) && > (p->flags & IORING_SETUP_SQPOLL)) > goto err; > > I don't really see how taking away SQPOLL from 32-bit tasks is > any better than just preventing access to the known-broken files > as Al suggested, or adding the hack to make it work as in > Christoph's original patch. That's why I'm hoping that Christoph's work and the discussion will reach consensus, but the bug should be patched in the end. IMHO, it's a good and easy enough fallback option (temporal?). > > Can we expect all existing and future user space to have a sane > fallback when IORING_SETUP_SQPOLL fails? SQPOLL has a few differences with non-SQPOLL modes, but it's easy to convert between them. Anyway, SQPOLL is a privileged special case that's here for performance/latency reasons, I don't think there will be any non-accidental users of it. -- Pavel Begunkov
