[PATCH 1/2] io_uring/waitid: honor task_work cancellation

[Hui Su <sh_def@163.com>]

io_waitid_cb() may run through the fallback task_work path when
task_work_add() can no longer queue work to the originating task. The
fallback runs from a kworker and io_uring marks such task work as
canceled through tw.cancel.

io_waitid_cb() currently ignores tw.cancel and calls __do_wait().
waitid is task-context dependent: __do_wait() performs child lookup
relative to current, and the retry path also uses
current->signal->wait_chldexit. If the callback runs from the fallback
kworker, current is therefore not the task that submitted the request.

Honor tw.cancel before entering __do_wait(). Complete the request with
-ECANCELED and skip the siginfo copy, since canceled task work may run
without the submitting task's userspace execution context.

Keep the existing siginfo handling for normal waitid completion and
explicit cancellation.

Fixes: f31ecf671ddc ("io_uring: add IORING_OP_WAITID support")
Cc: stable@vger.kernel.org
Signed-off-by: Hui Su <sh_def@163.com>
---
 io_uring/waitid.c | 16 ++++++++++++----
 1 file changed, 12 insertions(+), 4 deletions(-)

diff --git a/io_uring/waitid.c b/io_uring/waitid.c
index 32f68fd7fcdd..7a23befd2579 100644
--- a/io_uring/waitid.c
+++ b/io_uring/waitid.c
@@ -125,7 +125,7 @@ static void io_waitid_remove_wq(struct io_kiocb *req)
 	}
 }
 
-static void io_waitid_complete(struct io_kiocb *req, int ret)
+static void io_waitid_complete(struct io_kiocb *req, int ret, bool copy_si)
 {
 	struct io_waitid *iw = io_kiocb_to_cmd(req, struct io_waitid);
 
@@ -137,7 +137,10 @@ static void io_waitid_complete(struct io_kiocb *req, int ret)
 	hlist_del_init(&req->hash_node);
 	io_waitid_remove_wq(req);
 
-	ret = io_waitid_finish(req, ret);
+	if (copy_si)
+		ret = io_waitid_finish(req, ret);
+	else
+		io_waitid_free(req);
 	if (ret < 0)
 		req_set_fail(req);
 	io_req_set_res(req, ret, 0);
@@ -159,7 +162,7 @@ static bool __io_waitid_cancel(struct io_kiocb *req)
 	if (atomic_fetch_inc(&iw->refs) & IO_WAITID_REF_MASK)
 		return false;
 
-	io_waitid_complete(req, -ECANCELED);
+	io_waitid_complete(req, -ECANCELED, true);
 	io_req_queue_tw_complete(req, -ECANCELED);
 	return true;
 }
@@ -202,6 +205,11 @@ static void io_waitid_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 	int ret;
 
 	io_tw_lock(ctx, tw);
+	if (unlikely(tw.cancel)) {
+		io_waitid_complete(req, -ECANCELED, false);
+		io_req_task_complete(tw_req, tw);
+		return;
+	}
 
 	ret = __do_wait(&iwa->wo);
 
@@ -229,7 +237,7 @@ static void io_waitid_cb(struct io_tw_req tw_req, io_tw_token_t tw)
 		}
 	}
 
-	io_waitid_complete(req, ret);
+	io_waitid_complete(req, ret, true);
 	io_req_task_complete(tw_req, tw);
 }
 
-- 
2.54.0