io_uring: fix invalid flags for io_put_kbuf()

io_req_complete_failed() doesn't require callers to hold ->uring_lock,
use IO_URING_F_UNLOCKED version of io_put_kbuf(). The only affected
place is the fail path of io_apoll_task_func(). Also add a lockdep
annotation to catch such bugs in the future.

Fixes: 3b2b78a8 ("io_uring: extend provided buf return to fails")
Signed-off-by: NPavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/ccf602dbf8df3b6a8552a262d8ee0a13a086fbc7.1648212967.git.asml.silence@gmail.comSigned-off-by: NJens Axboe <axboe@kernel.dk>

fs/io_uring.c

@@ -1370,6 +1370,8 @@ static inline unsigned int io_put_kbuf(struct io_kiocb *req,
 		cflags = __io_put_kbuf(req, &ctx->io_buffers_comp);
 		spin_unlock(&ctx->completion_lock);
 	} else {
+		lockdep_assert_held(&req->ctx->uring_lock);
+
 		cflags = __io_put_kbuf(req, &req->ctx->io_buffers_cache);
 	}
 
@@ -2165,7 +2167,7 @@ static inline void io_req_complete(struct io_kiocb *req, s32 res)
 static void io_req_complete_failed(struct io_kiocb *req, s32 res)
 {
 	req_set_fail(req);
-	io_req_complete_post(req, res, io_put_kbuf(req, 0));
+	io_req_complete_post(req, res, io_put_kbuf(req, IO_URING_F_UNLOCKED));
 }
 
 static void io_req_complete_fail_submit(struct io_kiocb *req)