From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754584Ab3ARB1X (ORCPT ); Thu, 17 Jan 2013 20:27:23 -0500 Received: from mail-qc0-f169.google.com ([209.85.216.169]:42715 "EHLO mail-qc0-f169.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752020Ab3ARB1U (ORCPT ); Thu, 17 Jan 2013 20:27:20 -0500 Date: Thu, 17 Jan 2013 17:27:13 -0800 From: Tejun Heo To: Linus Torvalds Cc: Arjan van de Ven , Ming Lei , Alex Riesen , Alan Stern , Jens Axboe , USB list , Linux Kernel Mailing List , Rusty Russell Subject: [PATCH 3/3] async, kmod: warn on synchronous request_module() from async workers Message-ID: <20130118012713.GI16568@mtj.dyndns.org> References: <20130116025251.GM2668@htj.dyndns.org> <20130116032502.GN2668@htj.dyndns.org> <20130116164832.GP2668@htj.dyndns.org> <50F6DD4D.3070808@linux.intel.com> <20130116213032.GS2668@htj.dyndns.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Synchronous requet_module() from an async worker can lead to deadlock because module init path may invoke async_synchronize_full(). The async worker waits for request_module() to complete and the module loading waits for the async task to finish. This bug happened in the block layer because of default elevator auto-loading. Block layer has been updated not to do default elevator auto-loading and it has been decided to disallow synchronous request_module() from async workers. Trigger WARN_ON_ONCE() on synchronous request_module() from async workers. For more details, please refer to the following thread. http://thread.gmane.org/gmane.linux.kernel/1420814 Signed-off-by: Tejun Heo Reported-by: Alex Riesen Cc: Linus Torvalds Cc: Arjan van de Ven --- Linus, please note that I dropped system_state == SYSTEM_RUNNING condition from WARN_ON_ONCE() as the deadlock can happen during system init too - e.g. libata probing block device using async making block layer try to load default elevator from initramfs. Thanks. kernel/kmod.c | 9 +++++++++ 1 file changed, 9 insertions(+) diff --git a/kernel/kmod.c b/kernel/kmod.c index 1c317e3..028287e 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -38,6 +38,7 @@ #include #include #include +#include #include #include @@ -130,6 +131,14 @@ int __request_module(bool wait, const char *fmt, ...) #define MAX_KMOD_CONCURRENT 50 /* Completely arbitrary value - KAO */ static int kmod_loop_msg; + /* + * We don't allow synchronous module loading from async. Module + * init may invoke async_synchronize_full() which will end up + * waiting for this task which already is waiting for the module + * loading to complete, leading to a deadlock. + */ + WARN_ON_ONCE(wait && async_current_func(NULL, NULL)); + va_start(args, fmt); ret = vsnprintf(module_name, MODULE_NAME_LEN, fmt, args); va_end(args); -- 1.8.0.2