Re: [GIT PULL] io_uring fixes for 5.12-rc2

[Linus Torvalds <torvalds@linux-foundation.org>]

On Sat, Mar 6, 2021 at 8:25 AM Jens Axboe <axboe@kernel.dk> wrote:
>
> You're not, but creds is just one part of it. But I think we're OK
> saying "If you do unshare(CLONE_FILES) or CLONE_FS, then it's not
> going to impact async offload for your io_uring". IOW, you really
> should do that before setting up your ring(s).

Yeah, I think that one is solidly in a "don't do that then" thing.

Changing credentials is "normal use" - if you are a server process,
you may want to just make sure that you use different credentials for
different client requests etc.

But doing something like "I set up an io_uring for async work, and
then I dis-associated from my existing FS state entirely", that's not
normal. That's just a "you did something crazy, and you'll get crazy
results back, because the async part is fundamentally different from
the synchronous part".

It might be an option to just tear down the IO uring state entirely if
somebody does a "unshare(CLONE_FILES)", the same way unsharing the VM
(ie execve) does. But then it shouldn't even try to keep the state in
sync, it would just be "ok, your old io_uring is now simply gone".

I'm not sure it's even worth worrying about. Because at some point,
it's just "garbage in, garbage out".

               Linus