[PATCH 1/1] io_uring: actively cancel poll/timeouts on exit

[Pavel Begunkov <asml.silence@gmail.com>]

If io_ring_ctx_wait_and_kill() haven't killed all requests on the first
attempt, new timeouts or requests enqueued for polling may appear. They
won't be ever cancelled by io_ring_exit_work() unless we specifically
handle that case. That hangs of the exit work locking up grabbed by
io_uring resources.

Cc: <stable@vger.kernel.org> # 5.5+
Cc: Josef <josef.grieb@gmail.com>
Reported-by: Dmitry Kadashev <dkadashev@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 55 +++++++++++++++++++++++++++------------------------
 1 file changed, 29 insertions(+), 26 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index fbf747803dbc..c1acc668fe96 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8620,6 +8620,32 @@ static int io_remove_personalities(int id, void *p, void *data)
 	return 0;
 }
 
+static void io_cancel_defer_files(struct io_ring_ctx *ctx,
+				  struct task_struct *task,
+				  struct files_struct *files)
+{
+	struct io_defer_entry *de = NULL;
+	LIST_HEAD(list);
+
+	spin_lock_irq(&ctx->completion_lock);
+	list_for_each_entry_reverse(de, &ctx->defer_list, list) {
+		if (io_match_task(de->req, task, files)) {
+			list_cut_position(&list, &ctx->defer_list, &de->list);
+			break;
+		}
+	}
+	spin_unlock_irq(&ctx->completion_lock);
+
+	while (!list_empty(&list)) {
+		de = list_first_entry(&list, struct io_defer_entry, list);
+		list_del_init(&de->list);
+		req_set_fail_links(de->req);
+		io_put_req(de->req);
+		io_req_complete(de->req, -ECANCELED);
+		kfree(de);
+	}
+}
+
 static void io_ring_exit_work(struct work_struct *work)
 {
 	struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx,
@@ -8633,6 +8659,8 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_iopoll_try_reap_events(ctx);
+		io_poll_remove_all(ctx, NULL, NULL);
+		io_kill_timeouts(ctx, NULL, NULL);
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 	io_ring_ctx_free(ctx);
 }
@@ -8654,6 +8682,7 @@ static void io_ring_ctx_wait_and_kill(struct io_ring_ctx *ctx)
 		io_cqring_overflow_flush(ctx, true, NULL, NULL);
 	mutex_unlock(&ctx->uring_lock);
 
+	io_cancel_defer_files(ctx, NULL, NULL);
 	io_kill_timeouts(ctx, NULL, NULL);
 	io_poll_remove_all(ctx, NULL, NULL);
 
@@ -8716,32 +8745,6 @@ static bool io_cancel_task_cb(struct io_wq_work *work, void *data)
 	return ret;
 }
 
-static void io_cancel_defer_files(struct io_ring_ctx *ctx,
-				  struct task_struct *task,
-				  struct files_struct *files)
-{
-	struct io_defer_entry *de = NULL;
-	LIST_HEAD(list);
-
-	spin_lock_irq(&ctx->completion_lock);
-	list_for_each_entry_reverse(de, &ctx->defer_list, list) {
-		if (io_match_task(de->req, task, files)) {
-			list_cut_position(&list, &ctx->defer_list, &de->list);
-			break;
-		}
-	}
-	spin_unlock_irq(&ctx->completion_lock);
-
-	while (!list_empty(&list)) {
-		de = list_first_entry(&list, struct io_defer_entry, list);
-		list_del_init(&de->list);
-		req_set_fail_links(de->req);
-		io_put_req(de->req);
-		io_req_complete(de->req, -ECANCELED);
-		kfree(de);
-	}
-}
-
 static void io_uring_cancel_files(struct io_ring_ctx *ctx,
 				  struct task_struct *task,
 				  struct files_struct *files)
-- 
2.24.0