[PATCH 2/3] io_uring/uring_cmd: allow non-iopoll cmds with IORING_SETUP_IOPOLL

[Caleb Sander Mateos <csander@purestorage.com>]

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.

Allow uring_cmd requests to be issued to IORING_SETUP_IOPOLL io_urings
even if their files don't implement ->uring_cmd_iopoll(). For these
uring_cmd requests, skip initializing struct io_kiocb's iopoll fields,
don't insert the request into iopoll_list, and take the
io_req_complete_defer() or io_req_task_work_add() path in
__io_uring_cmd_done() instead of setting the iopoll_completed flag. Also
allow io_uring_cmd_mark_cancelable() to be called on these uring_cmds.
Assert that io_uring_cmd_mark_cancelable() is only called on
non-IORING_SETUP_IOPOLL io_urings or uring_cmds to files that don't
implement ->uring_cmd_iopoll().

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
---
 io_uring/io_uring.c  |  4 +++-
 io_uring/uring_cmd.c | 11 +++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index c45af82dda3d..4e68a5168894 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1417,11 +1417,13 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 
 	if (ret == IOU_ISSUE_SKIP_COMPLETE) {
 		ret = 0;
 
 		/* If the op doesn't have a file, we're not polling for it */
-		if ((req->ctx->flags & IORING_SETUP_IOPOLL) && def->iopoll_queue)
+		if ((req->ctx->flags & IORING_SETUP_IOPOLL) &&
+		    def->iopoll_queue && (!io_is_uring_cmd(req) ||
+					  req->file->f_op->uring_cmd_iopoll))
 			io_iopoll_req_issued(req, issue_flags);
 	}
 	return ret;
 }
 
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index ee7b49f47cb5..8df52e8f1c1b 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -108,12 +108,12 @@ void io_uring_cmd_mark_cancelable(struct io_uring_cmd *cmd,
 	 * Doing cancelations on IOPOLL requests are not supported. Both
 	 * because they can't get canceled in the block stack, but also
 	 * because iopoll completion data overlaps with the hash_node used
 	 * for tracking.
 	 */
-	if (ctx->flags & IORING_SETUP_IOPOLL)
-		return;
+	WARN_ON_ONCE(ctx->flags & IORING_SETUP_IOPOLL &&
+		     req->file->f_op->uring_cmd_iopoll);
 
 	if (!(cmd->flags & IORING_URING_CMD_CANCELABLE)) {
 		cmd->flags |= IORING_URING_CMD_CANCELABLE;
 		io_ring_submit_lock(ctx, issue_flags);
 		hlist_add_head(&req->hash_node, &ctx->cancelable_uring_cmd);
@@ -165,11 +165,12 @@ void __io_uring_cmd_done(struct io_uring_cmd *ioucmd, s32 ret, u64 res2,
 		if (req->ctx->flags & IORING_SETUP_CQE_MIXED)
 			req->cqe.flags |= IORING_CQE_F_32;
 		io_req_set_cqe32_extra(req, res2, 0);
 	}
 	io_req_uring_cleanup(req, issue_flags);
-	if (req->ctx->flags & IORING_SETUP_IOPOLL) {
+	if (req->ctx->flags & IORING_SETUP_IOPOLL &&
+	    req->file->f_op->uring_cmd_iopoll) {
 		/* order with io_iopoll_req_issued() checking ->iopoll_complete */
 		smp_store_release(&req->iopoll_completed, 1);
 	} else if (issue_flags & IO_URING_F_COMPLETE_DEFER) {
 		if (WARN_ON_ONCE(issue_flags & IO_URING_F_UNLOCKED))
 			return;
@@ -255,13 +256,11 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 		issue_flags |= IO_URING_F_SQE128;
 	if (ctx->flags & (IORING_SETUP_CQE32 | IORING_SETUP_CQE_MIXED))
 		issue_flags |= IO_URING_F_CQE32;
 	if (io_is_compat(ctx))
 		issue_flags |= IO_URING_F_COMPAT;
-	if (ctx->flags & IORING_SETUP_IOPOLL) {
-		if (!file->f_op->uring_cmd_iopoll)
-			return -EOPNOTSUPP;
+	if (ctx->flags & IORING_SETUP_IOPOLL && file->f_op->uring_cmd_iopoll) {
 		issue_flags |= IO_URING_F_IOPOLL;
 		req->iopoll_completed = 0;
 		if (ctx->flags & IORING_SETUP_HYBRID_IOPOLL) {
 			/* make sure every req only blocks once */
 			req->flags &= ~REQ_F_IOPOLL_STATE;
-- 
2.45.2