On Wed, Nov 27, 2024 at 02:51:26PM -0700, Jens Axboe wrote: > On Wed, Nov 27, 2024 at 2:27?PM Kent Overstreet <kent.overstreet@xxxxxxxxx> wrote: > > > > On Wed, Nov 27, 2024 at 02:16:24PM -0700, Jens Axboe wrote: > > > I'd argue the fact that you are using an mm from a different process > > > without grabbing a reference is the wrinkle. I just don't think it's a > > > problem right now, but it could be... aio is tied to the mm because of > > > how it does completions, potentially, and hence needs this exit_aio() > > > hack because of that. aio also doesn't care, because it doesn't care > > > about blocking - it'll happily block during issue. > > > > I'm not trying to debate who's bug it is, I'm just checking if I need to > > backport a security fix. > > Not trying to place blame. > > > > > Jens, is it really FMODE_NOWAIT that controls whether we can hit this? A > > > > very cursory glance leads me to suspect "no", it seems like this is a > > > > bug if io_uring is allowed on bcachefs at all. > > > > > > I just looked at bcachefs dio writes, which look to be the only case of > > > this. And yes, for writes, if FMODE_NOWAIT isn't set, then io-wq is > > > always involved for the IO. > > > > Ok, sounds like we're in the clear. I already started writing the > > patch, so it'll just be a "now we can turn on FMODE_NOWAIT" instead of > > a bugfix. > > That sounds good - and FMODE_NOWAIT will be a good addition. It'll make > RWF_NOWAIT work, and things like io_uring will also work better as it > won't need to needlessly punt to an io-wq worker to complete this IO. > > > By the way, did the lifetime issue that was causing umount/remount to > > fail ever get resolved? I've currently got no test coverage for > > io_uring, would be nice to flip that back on. > > Nope, I do have an updated branch since then, but it's still sitting > waiting on getting a bit more love. I suspect it'll be done for 6.14. Alright - if you want to ping me when that's ready, along with any other knobs I should flip on for io_uring support, I'll flip io_uring back on in my test infrastructure at that time.
