From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 545C7C43387 for ; Tue, 8 Jan 2019 20:10:01 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2628120827 for ; Tue, 8 Jan 2019 20:10:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546978201; bh=HkM9043lStGDH3UILF6n4HWAV5IcMSXu9LrCFF+VHPs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=Zu3exWaDnVMvAz3MG1TKTeZGo2AtEsFtAvsrEv+2NT4/KaB4FCalhzxTC0IzbAeTn yrDN6i0TTm3vIPVxpOAc9XypB2SsERkwmL5TiqX4g8kERZpHCdgt5KNXAHgq3J2X+I Efd4VXzr7gi2wFs0oA0v19vzxb8aEwlLQmmzz5gM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733110AbfAHUJ7 (ORCPT ); Tue, 8 Jan 2019 15:09:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:60950 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729277AbfAHT0w (ORCPT ); Tue, 8 Jan 2019 14:26:52 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 5D2C02087F; Tue, 8 Jan 2019 19:26:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1546975612; bh=HkM9043lStGDH3UILF6n4HWAV5IcMSXu9LrCFF+VHPs=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=tRWfaq9R0GerKEQveJVEDWlZSAW6mFAxC42rCFeAMMCkjQDO1PJWXjkCfSv06OhQU cMNDgfMSNeK3tfTrn/oktDamRjHx7OIb5yCYOzgcelqhm6Ow5YsFzAjCVXw7xaHUhq 0v7JoxF/x31Cf7At7KynDR5Gs3dThzk38mvJ7lpA= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Anders Roxell , Arnd Bergmann , Greg Kroah-Hartman , Sasha Levin Subject: [PATCH AUTOSEL 4.20 013/117] writeback: don't decrement wb->refcnt if !wb->bdi Date: Tue, 8 Jan 2019 14:24:41 -0500 Message-Id: <20190108192628.121270-13-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190108192628.121270-1-sashal@kernel.org> References: <20190108192628.121270-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Anders Roxell [ Upstream commit 347a28b586802d09604a149c1a1f6de5dccbe6fa ] This happened while running in qemu-system-aarch64, the AMBA PL011 UART driver when enabling CONFIG_DEBUG_TEST_DRIVER_REMOVE. arch_initcall(pl011_init) came before subsys_initcall(default_bdi_init), devtmpfs' handle_remove() crashes because the reference count is a NULL pointer only because wb->bdi hasn't been initialized yet. Rework so that wb_put have an extra check if wb->bdi before decrement wb->refcnt and also add a WARN_ON_ONCE to get a warning if it happens again in other drivers. Fixes: 52ebea749aae ("writeback: make backing_dev_info host cgroup-specific bdi_writebacks") Co-developed-by: Arnd Bergmann Signed-off-by: Arnd Bergmann Signed-off-by: Anders Roxell Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- include/linux/backing-dev-defs.h | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h index 9a6bc0951cfa..c31157135598 100644 --- a/include/linux/backing-dev-defs.h +++ b/include/linux/backing-dev-defs.h @@ -258,6 +258,14 @@ static inline void wb_get(struct bdi_writeback *wb) */ static inline void wb_put(struct bdi_writeback *wb) { + if (WARN_ON_ONCE(!wb->bdi)) { + /* + * A driver bug might cause a file to be removed before bdi was + * initialized. + */ + return; + } + if (wb != &wb->bdi->wb) percpu_ref_put(&wb->refcnt); } -- 2.19.1