io_uring: complete request via task work in case of DEFER_TASKRUN

So far io_req_complete_post() only covers DEFER_TASKRUN by completing
request via task work when the request is completed from IOWQ.

However, uring command could be completed from any context, and if io
uring is setup with DEFER_TASKRUN, the command is required to be
completed from current context, otherwise wait on IORING_ENTER_GETEVENTS
can't be wakeup, and may hang forever.

The issue can be observed on removing ublk device, but turns out it is
one generic issue for uring command & DEFER_TASKRUN, so solve it in
io_uring core code.

Fixes: e6aeb27 ("io_uring: complete all requests in task context")
Cc: [email protected]
Link: https://lore.kernel.org/linux-block/[email protected]/
Reported-by: Jens Axboe <[email protected]>
Cc: Kanchan Joshi <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

Author: Ming Lei

io_uring/io_uring.c

@@ -998,7 +998,7 @@ static void __io_req_complete_post(struct io_kiocb *req)
 
 void io_req_complete_post(struct io_kiocb *req, unsigned issue_flags)
 {
-	if (req->ctx->task_complete && (issue_flags & IO_URING_F_IOWQ)) {
+	if (req->ctx->task_complete && req->ctx->submitter_task != current) {
 		req->io_task_work.func = io_req_task_complete;
 		io_req_task_work_add(req);
 	} else if (!(issue_flags & IO_URING_F_UNLOCKED) ||