[PATCH v2 6/6] io_uring: warn when ring exit takes too long

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

We use system_unbound_wq to run io_ring_exit_work(), so it's hard to
monitor whether removal hang or not. Add WARN_ONCE to catch hangs.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
 fs/io_uring.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 92ba3034de64..623563b817f7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -8554,6 +8554,8 @@ static void io_ring_exit_work(struct work_struct *work)
 	struct io_ring_ctx *ctx = container_of(work, struct io_ring_ctx, exit_work);
 	struct io_tctx_exit exit;
 	struct io_tctx_node *node;
+	const u64 bias_ms = MSEC_PER_SEC * 60 * 5;
+	ktime_t start = ktime_get();
 	int ret;
 
 	/*
@@ -8564,10 +8566,13 @@ static void io_ring_exit_work(struct work_struct *work)
 	 */
 	do {
 		io_uring_try_cancel_requests(ctx, NULL, NULL);
+		WARN_ON_ONCE(ktime_ms_delta(ktime_get(), start) > bias_ms);
 	} while (!wait_for_completion_timeout(&ctx->ref_comp, HZ/20));
 
 	mutex_lock(&ctx->uring_lock);
 	while (!list_empty(&ctx->tctx_list)) {
+		WARN_ON_ONCE(ktime_ms_delta(ktime_get(), start) > bias_ms);
+
 		node = list_first_entry(&ctx->tctx_list, struct io_tctx_node,
 					ctx_node);
 		exit.ctx = ctx;
-- 
2.24.0