Re: [PATCH v3 0/4] io_uring/uring_cmd: allow non-iopoll cmds with IORING_SETUP_IOPOLL

[Caleb Sander Mateos]

On Fri, Feb 20, 2026 at 6:25 AM Ming Lei <ming.lei@xxxxxxxxxx> wrote:
>
> On Thu, Feb 19, 2026 at 10:22:23AM -0700, Caleb Sander Mateos wrote:
> > Currently, creating an io_uring with IORING_SETUP_IOPOLL requires all
> > requests issued to it to support iopoll. This prevents, for example,
> > using ublk zero-copy together with IORING_SETUP_IOPOLL, as ublk
> > zero-copy buffer registrations are performed using a uring_cmd. There's
> > no technical reason why these non-iopoll uring_cmds can't be supported.
> > They will either complete synchronously or via an external mechanism
> > that calls io_uring_cmd_done(), so they don't need to be polled.
>
> For sync uring command, it is fine to support for IOPOLL.
>
> However, there are async uring command, which may be completed in irq
> context, or in multishot way, at least the later isn't supported in
> io_do_iopoll() yet.

Can you describe the issues you envision in more detail?

io_uring_cmd_done() can already be called in irq context. Even if the
request is not REQ_F_IOPOLL, any completion from irq context must call
io_uring_cmd_done() with IO_URING_F_UNLOCKED because an interrupt
handler can't acquire a mutex. That means the completion will be via
task work. The mutex acquisition in io_uring_cmd_del_cancelable()
would be a problem in irq context, so ->uring_cmd() implementations
that use io_uring_cmd_mark_cancelable() will have to call
io_uring_cmd_done() from task context, which both ublk and fuse
already do.

I missed that the SOCKET_URING_OP_TX_TIMESTAMP uring_cmd may use
apoll, so that one will probably have to be prohibited on
IORING_SETUP_IOPOLL io_urings.

Best,
Caleb