io_uring: find and cancel head link async work on files exit

Commit f254ac04 ("io_uring: enable lookup of links holding inflight files")
only handled 2 out of the three head link cases we have, we also need to
lookup and cancel work that is blocked in io-wq if that work has a link
that's holding a reference to the files structure.

Put the "cancel head links that hold this request pending" logic into
io_attempt_cancel(), which will to through the motions of finding and
canceling head links that hold the current inflight files stable request
pending.

Cc: stable@vger.kernel.org
Reported-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -8063,6 +8063,33 @@ static bool io_timeout_remove_link(struct io_ring_ctx *ctx,
 	return found;
 }
 
+static bool io_cancel_link_cb(struct io_wq_work *work, void *data)
+{
+	return io_match_link(container_of(work, struct io_kiocb, work), data);
+}
+
+static void io_attempt_cancel(struct io_ring_ctx *ctx, struct io_kiocb *req)
+{
+	enum io_wq_cancel cret;
+
+	/* cancel this particular work, if it's running */
+	cret = io_wq_cancel_work(ctx->io_wq, &req->work);
+	if (cret != IO_WQ_CANCEL_NOTFOUND)
+		return;
+
+	/* find links that hold this pending, cancel those */
+	cret = io_wq_cancel_cb(ctx->io_wq, io_cancel_link_cb, req, true);
+	if (cret != IO_WQ_CANCEL_NOTFOUND)
+		return;
+
+	/* if we have a poll link holding this pending, cancel that */
+	if (io_poll_remove_link(ctx, req))
+		return;
+
+	/* final option, timeout link is holding this req pending */
+	io_timeout_remove_link(ctx, req);
+}
+
 static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				  struct files_struct *files)
 {
@@ -8116,10 +8143,8 @@ static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				continue;
 			}
 		} else {
-			io_wq_cancel_work(ctx->io_wq, &cancel_req->work);
-			/* could be a link, check and remove if it is */
-			if (!io_poll_remove_link(ctx, cancel_req))
-				io_timeout_remove_link(ctx, cancel_req);
+			/* cancel this request, or head link requests */
+			io_attempt_cancel(ctx, cancel_req);
 			io_put_req(cancel_req);
 		}