io_uring: don't prepare DRAIN reqs twice

If req->io is not NULL, it's already prepared. Don't do it again,
it's dangerous.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 79c90eb..51be073 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5014,12 +5014,13 @@ static int io_req_defer(struct io_kiocb *req, const struct io_uring_sqe *sqe)
        if (!req_need_defer(req) && list_empty_careful(&ctx->defer_list))
                return 0;
 
-       if (!req->io && io_alloc_async_ctx(req))
-               return -EAGAIN;
-
-       ret = io_req_defer_prep(req, sqe);
-       if (ret < 0)
-               return ret;
+       if (!req->io) {
+               if (io_alloc_async_ctx(req))
+                       return -EAGAIN;
+               ret = io_req_defer_prep(req, sqe);
+               if (ret < 0)
+                       return ret;
+       }
 
        spin_lock_irq(&ctx->completion_lock);
        if (!req_need_defer(req) && list_empty(&ctx->defer_list)) {