From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968036AbcA0U4f (ORCPT ); Wed, 27 Jan 2016 15:56:35 -0500 Received: from youngberry.canonical.com ([91.189.89.112]:43639 "EHLO youngberry.canonical.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1161078AbcA0UkC (ORCPT ); Wed, 27 Jan 2016 15:40:02 -0500 From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Ani Sinha , "Paul E. McKenney" , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 217/268] sysrq: Fix warning in sysrq generated crash. Date: Wed, 27 Jan 2016 12:34:38 -0800 Message-Id: <1453926929-17663-218-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1453926929-17663-1-git-send-email-kamal@canonical.com> References: <1453926929-17663-1-git-send-email-kamal@canonical.com> X-Extended-Stable: 4.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.2.8-ckt3 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Ani Sinha commit 984cf355aeaa8f2eda3861b50d0e8d3e3f77e83b upstream. Commit 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq") replaced spin_lock_irqsave() calls with rcu_read_lock() calls in sysrq. Since rcu_read_lock() does not disable preemption, faulthandler_disabled() in __do_page_fault() in x86/fault.c returns false. When the code later calls might_sleep() in the pagefault handler, we get the following warning: BUG: sleeping function called from invalid context at ../arch/x86/mm/fault.c:1187 in_atomic(): 0, irqs_disabled(): 0, pid: 4706, name: bash Preemption disabled at:[] printk+0x48/0x4a To fix this, we release the RCU read lock before we crash. Tested this patch on linux 3.18 by booting off one of our boards. Fixes: 984d74a72076a1 ("sysrq: rcu-ify __handle_sysrq") Signed-off-by: Ani Sinha Reviewed-by: Rik van Riel Signed-off-by: Paul E. McKenney Signed-off-by: Kamal Mostafa --- drivers/tty/sysrq.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index b5b4278..e54c7c7 100644 --- a/drivers/tty/sysrq.c +++ b/drivers/tty/sysrq.c @@ -133,6 +133,12 @@ static void sysrq_handle_crash(int key) { char *killer = NULL; + /* we need to release the RCU read lock here, + * otherwise we get an annoying + * 'BUG: sleeping function called from invalid context' + * complaint from the kernel before the panic. + */ + rcu_read_unlock(); panic_on_oops = 1; /* force panic */ wmb(); *killer = 1; -- 1.9.1