[PATCH 1/2] io_uring: fix work_exit sqpoll cancellations

[PATCH 1/2] io_uring: fix work_exit sqpoll cancellations

[Pavel Begunkov]

After closing an SQPOLL ring, io_ring_exit_work() kicks in and starts
doing cancellations via io_uring_try_cancel_requests(). It will go
through io_uring_try_cancel_iowq(), which uses ctx->tctx_list, but as
SQPOLL task don't have a ctx note, its io-wq won't be reachable and so
is left not cancelled.

It will eventually cancelled when one of the tasks dies, but if a thread
group survives for long and changes rings, it will spawn lots of
unreclaimed resources and live locked works.

Cancel SQPOLL task's io-wq separately in io_ring_exit_work().

Cc: stable@vger.kernel.org
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index eef373394ee9..640a4bc77aa6 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8678,6 +8678,13 @@ static void io_tctx_exit_cb(struct callback_head *cb)
 	complete(&work->completion);
 }
 
+static bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
+{
+	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
+
+	return req->ctx == data;
+}
+
 static void io_ring_exit_work(struct work_struct *work)
 {
 	struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, exit_work);
@@ -8694,6 +8701,17 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_uring_try_cancel_requests(ctx, NULL, NULL);
+		if (ctx->sq_data) {
+			struct io_sq_data *sqd = ctx->sq_data;
+			struct task_struct *tsk;
+
+			io_sq_thread_park(sqd);
+			tsk = sqd->thread;
+			if (tsk && tsk->io_uring && tsk->io_uring->io_wq)
+				io_wq_cancel_cb(tsk->io_uring->io_wq,
+						io_cancel_ctx_cb, ctx, true);
+			io_sq_thread_unpark(sqd);
+		}
 
 		WARN_ON_ONCE(time_after(jiffies, timeout));
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
@@ -8843,13 +8861,6 @@ static bool io_cancel_defer_files(struct io_ring_ctx *ctx,
 	return true;
 }
 
-static bool io_cancel_ctx_cb(struct io_wq_work *work, void *data)
-{
-	struct io_kiocb *req = container_of(work, struct io_kiocb, work);
-
-	return req->ctx == data;
-}
-
 static bool io_uring_try_cancel_iowq(struct io_ring_ctx *ctx)
 {
 	struct io_tctx_node *node;
-- 
2.31.1