From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932312AbbLRNGa (ORCPT ); Fri, 18 Dec 2015 08:06:30 -0500 Received: from e32.co.us.ibm.com ([32.97.110.150]:42570 "EHLO e32.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932270AbbLRNGZ (ORCPT ); Fri, 18 Dec 2015 08:06:25 -0500 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org Date: Fri, 18 Dec 2015 05:01:25 -0800 From: "Paul E. McKenney" To: Ani Sinha Cc: Ani Sinha , Greg Kroah-Hartman , Jiri Slaby , linux-kernel@vger.kernel.org, Rik van Riel , Ivan Delalande , Francesco Ruggeri Subject: Re: [PATCH 1/1] Fix 'sleeping function called from invalid context' warning in sysrq generated crash. Message-ID: <20151218130125.GO4054@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <1450401310-29117-1-git-send-email-ani@arista.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1450401310-29117-1-git-send-email-ani@arista.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15121813-0005-0000-0000-00001ABA7DC8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 17, 2015 at 05:15:10PM -0800, Ani Sinha wrote: > 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 I queued this with Rik's Signed-off-by, and fixed some checkpatch.pl errors. Please run scripts/checkpatch.pl on your patches in the future. Please see below for the result. Rik, did you test this as well? If so, may I also have your Tested-by? Thanx, Paul ------------------------------------------------------------------------ commit c95a158356397844a5a6deb0bd58758084f891df Author: Ani Sinha Date: Thu Dec 17 17:15:10 2015 -0800 sysrq: Fix warning in sysrq generated crash. 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 diff --git a/drivers/tty/sysrq.c b/drivers/tty/sysrq.c index 5381a728d23e..e5139402e7f8 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;