From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:37282 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933478AbeAKOWx (ORCPT ); Thu, 11 Jan 2018 09:22:53 -0500 Subject: Patch "sysrq: Fix warning in sysrq generated crash." has been added to the 4.4-stable tree To: ani@arista.com, dbueso@suse.de, gregkh@linuxfoundation.org, paulmck@linux.vnet.ibm.com, riel@redhat.com Cc: , From: Date: Thu, 11 Jan 2018 15:22:23 +0100 Message-ID: <151568054323233@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled sysrq: Fix warning in sysrq generated crash. to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: sysrq-fix-warning-in-sysrq-generated-crash.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 984cf355aeaa8f2eda3861b50d0e8d3e3f77e83b Mon Sep 17 00:00:00 2001 From: Ani Sinha Date: Thu, 17 Dec 2015 17:15:10 -0800 Subject: sysrq: Fix warning in sysrq generated crash. 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: Davidlohr Bueso Signed-off-by: Greg Kroah-Hartman --- drivers/tty/sysrq.c | 6 ++++++ 1 file changed, 6 insertions(+) --- 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; Patches currently in stable-queue which might be from ani@arista.com are queue-4.4/sysrq-fix-warning-in-sysrq-generated-crash.patch