On 7/24/23 12:01?PM, Linus Torvalds wrote: > On Mon, 24 Jul 2023 at 10:46, Christian Brauner <brauner@xxxxxxxxxx> wrote: >> >> I don't think we do but it's something to keep in mind with async io >> interfaces where the caller is free to create other threads after having >> registered a request. Depending on how file references are done things >> can get tricky easily. > > Honestly, by now, the io_uring code had *better* understand that it > needs to act exactly like a user thread. > > Anything else is simply not acceptable. io_uring has been a huge pain, > and the only thing that salvaged the horror was that the io_uring > async code should now *always* be done as a real thread. > > If io_uring does something from truly async context (ie interrupts, > not io_uring threads), then io_uring had better be very *very* > careful. > > And any kind of "from kthread context" is not acceptable. We've been > there, done that, and have the battle scars. Never again. > > So the absolutely *only* acceptable context is "I'm a real > io_uringthread that looks exactly like a user thread in every which > way, except I never return to user space". > > And if io_uring does absolutely _anything_ to file descriptors from > any other context, it needs to be fixed *NOW*. io_uring never does that isn't the original user space creator task, or from the io-wq workers that it may create. Those are _always_ normal threads. There's no workqueue/kthread usage for IO or file getting/putting/installing/removing etc. -- Jens Axboe
