From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-lj1-f197.google.com (mail-lj1-f197.google.com [209.85.208.197]) by kanga.kvack.org (Postfix) with ESMTP id D1B566B0494 for ; Tue, 30 Oct 2018 07:36:35 -0400 (EDT) Received: by mail-lj1-f197.google.com with SMTP id e11-v6so4201741lji.23 for ; Tue, 30 Oct 2018 04:36:35 -0700 (PDT) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id y206sor3327092lfa.42.2018.10.30.04.36.33 for (Google Transport Security); Tue, 30 Oct 2018 04:36:33 -0700 (PDT) From: Anders Roxell Subject: [PATCH v2 2/2] writeback: don't decrement wb->refcnt if !wb->bdi Date: Tue, 30 Oct 2018 12:35:45 +0100 Message-Id: <20181030113545.30999-2-anders.roxell@linaro.org> In-Reply-To: <20181030113545.30999-1-anders.roxell@linaro.org> References: <20181030113545.30999-1-anders.roxell@linaro.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: owner-linux-mm@kvack.org List-ID: To: linux@armlinux.org.uk, gregkh@linuxfoundation.org, akpm@linux-foundation.org Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org, tj@kernel.org, Anders Roxell , Arnd Bergmann 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 --- 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