From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934734AbbLRBPu (ORCPT ); Thu, 17 Dec 2015 20:15:50 -0500 Received: from mail-pa0-f47.google.com ([209.85.220.47]:33106 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934615AbbLRBPr (ORCPT ); Thu, 17 Dec 2015 20:15:47 -0500 From: Ani Sinha To: Ani Sinha , Greg Kroah-Hartman , Jiri Slaby , linux-kernel@vger.kernel.org, Paul McKenney , Rik van Riel , Ivan Delalande , Francesco Ruggeri Cc: Ani Sinha Subject: [PATCH 1/1] Fix 'sleeping function called from invalid context' warning in sysrq generated crash. Date: Thu, 17 Dec 2015 17:15:10 -0800 Message-Id: <1450401310-29117-1-git-send-email-ani@arista.com> X-Mailer: git-send-email 1.8.1.4 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 --- drivers/tty/sysrq.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 5381a72..08987ad 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; -- 1.8.1.4