[PATCH 2/2] io_uring: add reschedule point to handle_tw_list()

[Jens Axboe <axboe@kernel.dk>]

If CONFIG_PREEMPT_NONE is set and the task_work chains are long, we
could be running into issues blocking others for too long. Add a
reschedule check in handle_tw_list(), and flush the ctx if we need to
reschedule.

Cc: stable@vger.kernel.org # 5.10+
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index bb8a532b051e..bc8845de2829 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1179,10 +1179,16 @@ static unsigned int handle_tw_list(struct llist_node *node,
 			/* if not contended, grab and improve batching */
 			*locked = mutex_trylock(&(*ctx)->uring_lock);
 			percpu_ref_get(&(*ctx)->refs);
-		}
+		} else if (!*locked)
+			*locked = mutex_trylock(&(*ctx)->uring_lock);
 		req->io_task_work.func(req, locked);
 		node = next;
 		count++;
+		if (unlikely(need_resched())) {
+			ctx_flush_and_put(*ctx, locked);
+			*ctx = NULL;
+			cond_resched();
+		}
 	}
 
 	return count;
-- 
2.39.0