From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753359AbbKOCHv (ORCPT ); Sat, 14 Nov 2015 21:07:51 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:35136 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752061AbbKOCEt (ORCPT ); Sat, 14 Nov 2015 21:04:49 -0500 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "poma" , "Peter Zijlstra" , "Rusty Russell" Date: Sun, 15 Nov 2015 01:45:45 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 02/60] module: Fix locking in symbol_put_addr() In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.247 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.73-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra commit 275d7d44d802ef271a42dc87ac091a495ba72fc5 upstream. Poma (on the way to another bug) reported an assertion triggering: [] module_assert_mutex_or_preempt+0x49/0x90 [] __module_address+0x32/0x150 [] __module_text_address+0x16/0x70 [] symbol_put_addr+0x29/0x40 [] dvb_frontend_detach+0x7d/0x90 [dvb_core] Laura Abbott produced a patch which lead us to inspect symbol_put_addr(). This function has a comment claiming it doesn't need to disable preemption around the module lookup because it holds a reference to the module it wants to find, which therefore cannot go away. This is wrong (and a false optimization too, preempt_disable() is really rather cheap, and I doubt any of this is on uber critical paths, otherwise it would've retained a pointer to the actual module anyway and avoided the second lookup). While its true that the module cannot go away while we hold a reference on it, the data structure we do the lookup in very much _CAN_ change while we do the lookup. Therefore fix the comment and add the required preempt_disable(). Reported-by: poma Signed-off-by: Peter Zijlstra (Intel) Signed-off-by: Rusty Russell Fixes: a6e6abd575fc ("module: remove module_text_address()") Signed-off-by: Ben Hutchings --- kernel/module.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) --- a/kernel/module.c +++ b/kernel/module.c @@ -893,11 +893,15 @@ void symbol_put_addr(void *addr) if (core_kernel_text(a)) return; - /* module_text_address is safe here: we're supposed to have reference - * to module from symbol_get, so it can't go away. */ + /* + * Even though we hold a reference on the module; we still need to + * disable preemption in order to safely traverse the data structure. + */ + preempt_disable(); modaddr = __module_text_address(a); BUG_ON(!modaddr); module_put(modaddr); + preempt_enable(); } EXPORT_SYMBOL_GPL(symbol_put_addr);