Re: [RFC net-next v3 23/29] io_uring: allow to pass addr into sendzc

[Pavel Begunkov]

On 8/15/22 14:30, Stefan Metzmacher wrote:
[...]
> > > that causes io_ring_exit_work() to wait for it.> It would be great if you or someone else could explain this in detail
> > > and maybe adding some comments into the code.
> >
> > Almost, the mechanism is absolutely the same as with requests,
> > and notifiers are actually requests for internal purposes.
> >
> > In __io_alloc_req_refill() we grab ctx->refs, which are waited
> > for in io_ring_exit_work(). We usually put requests into a cache,
> > so when a request is complete we don't put the ref and therefore
> > in io_ring_exit_work() we also have a call to io_req_caches_free(),
> > which puts ctx->refs.
>
> Ok, thanks.
>
> Would a close() on the ring fd block? I guess not, but the exit_work may block, correct?

Right, close doesn't block, it queues exit_work to get executed async.
exit_work() will wait for ctx->refs and then will free most of
io_uring resources.

> So a process would be a zombie until net released all references?

The userspace process will exit normally, but you can find a kernel
thread (kworker) doing the job.

--
Pavel Begunkov