io_uring: fix possible deadlock in io_register_iowq_max_workers()

commit 73254a297c2dd094abec7c9efee32455ae875bdf upstream.

The io_register_iowq_max_workers() function calls io_put_sq_data(), which acquires the sqd->lock without releasing the uring_lock. Similar to the commit 009ad9f0c6ee ("io_uring: drop ctx->uring_lock before acquiring sqd->lock"), this can lead to a potential deadlock situation.

To resolve this issue, the uring_lock is released before calling io_put_sq_data(), and then it is re-acquired after the function call.

This change ensures that the locks are acquired in the correct order, preventing the possibility of a deadlock.

---
 io_uring/io_uring.c | 5 +++++
 1 file changed, 5 insertions(+)

index 484c9bcbee77..70dd6a5b9647 100644
@@ -4358,8 +4358,10 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	}
 
 	if (sqd) {
+		mutex_unlock(&ctx->uring_lock);
 		mutex_unlock(&sqd->lock);
 		io_put_sq_data(sqd);
+		mutex_lock(&ctx->uring_lock);
 	}
 
 	if (copy_to_user(arg, new_count, sizeof(new_count)))

@@ -4384,8 +4386,11 @@ static __cold int io_register_iowq_max_workers(struct io_ring_ctx *ctx,
 	return 0;
 err:
 	if (sqd) {
+		mutex_unlock(&ctx->uring_lock);
 		mutex_unlock(&sqd->lock);
 		io_put_sq_data(sqd);
+		mutex_lock(&ctx->uring_lock);
+
 	}
 	return ret;
 }

2.40.1