Re: [PATCH 6.12.y 11/15] io_uring/msg_ring: ensure io_kiocb freeing is deferred for RCU

[Greg KH <greg@kroah.com>]

On Sat, Sep 06, 2025 at 07:47:00AM +0530, Harshit Mogalapalli wrote:
> Hi Jens,
> 
> 
> On 06/09/25 01:28, Jens Axboe wrote:
> > On 9/5/25 5:04 AM, Harshit Mogalapalli wrote:
> > > diff --git a/include/linux/io_uring_types.h b/include/linux/io_uring_types.h
> > > index 5ce332fc6ff5..3b27d9bcf298 100644
> > > --- a/include/linux/io_uring_types.h
> > > +++ b/include/linux/io_uring_types.h
> > > @@ -648,6 +648,8 @@ struct io_kiocb {
> > >   	struct io_task_work		io_task_work;
> > >   	/* for polled requests, i.e. IORING_OP_POLL_ADD and async armed poll */
> > >   	struct hlist_node		hash_node;
> > > +	/* for private io_kiocb freeing */
> > > +	struct rcu_head		rcu_head;
> > >   	/* internal polling, see IORING_FEAT_FAST_POLL */
> > >   	struct async_poll		*apoll;
> > >   	/* opcode allocated if it needs to store data for async defer */
> > 
> 
> Thanks a lot for looking into this one.
> 
> > This should go into a union with hash_node, rather than bloat the
> > struct. That's how it was done upstream, not sure why this one is
> > different?
> > 
> 
> We don't have commit: 01ee194d1aba ("io_uring: add support for hybrid
> IOPOLL") which moves hlist_node	to a union along with iopoll_start,
> 
>         struct io_task_work             io_task_work;
> -       /* for polled requests, i.e. IORING_OP_POLL_ADD and async armed poll
> */
> -       struct hlist_node               hash_node;
> +       union {
> +               /*
> +                * for polled requests, i.e. IORING_OP_POLL_ADD and async
> armed
> +                * poll
> +                */
> +               struct hlist_node       hash_node;
> +               /* For IOPOLL setup queues, with hybrid polling */
> +               u64                     iopoll_start;
> +       };
> 
> 
> given that we don't need the above commit, and partly because I didn't
> realize about the bloat benefit we would get I added rcu_head without a
> union. Thanks a lot for correctly. I will check the size bloat next time
> when I run into this situation.
> 
> Thank you very much for correcting this and providing a backport.
> 
> Greg/Sasha: Should I send a v2 of this series with my backport swapped with
> the one from Jens ?

I just took Jens's patch.  So I'll drop your patch from this series too.

thanks,

greg k-h