Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932798AbbKLXZb (ORCPT ); Thu, 12 Nov 2015 18:25:31 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:45637 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932708AbbKLXT6 (ORCPT ); Thu, 12 Nov 2015 18:19:58 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: "Peter Zijlstra (Intel)" , Rusty Russell , Kamal Mostafa Subject: [PATCH 3.19.y-ckt 136/155] module: Fix locking in symbol_put_addr() Date: Thu, 12 Nov 2015 15:18:10 -0800 Message-Id: <1447370309-357-137-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1447370309-357-1-git-send-email-kamal@canonical.com> References: <1447370309-357-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 3.19 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2597 Lines: 71 3.19.8-ckt10 -stable 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: Kamal Mostafa --- kernel/module.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-) diff --git a/kernel/module.c b/kernel/module.c index bc8d162..8942456 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -906,11 +906,15 @@ 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); -- 1.9.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/