From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755870AbaLHPI4 (ORCPT ); Mon, 8 Dec 2014 10:08:56 -0500 Received: from smtprelay0094.hostedemail.com ([216.40.44.94]:36485 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755661AbaLHPIz (ORCPT ); Mon, 8 Dec 2014 10:08:55 -0500 X-Session-Marker: 6E657665747340676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1539:1593:1594:1711:1730:1747:1777:1792:2194:2199:2393:2553:2559:2562:3138:3139:3140:3141:3142:3352:3622:3865:3866:3867:3870:3871:3874:4250:5007:6261:7556:7875:10004:10400:10848:10967:11232:11658:11914:12296:12517:12519:12740:13069:13255:13311:13357:21080,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:fn,MSBL:0,DNSBL:none,Custom_rules:0:0:0 X-HE-Tag: shirt83_3082013c7703a X-Filterd-Recvd-Size: 1620 Date: Mon, 8 Dec 2014 10:08:51 -0500 From: Steven Rostedt To: Linus Torvalds Cc: LKML , Ingo Molnar , Thomas Gleixner , Jiri Kosina , Petr Mladek Subject: Re: [GIT PULL] tracing/NMI/printk: Use seq_buf for safe printing from NMI context Message-ID: <20141208100851.3906cc0a@gandalf.local.home> In-Reply-To: <20141208100528.5f97106f@gandalf.local.home> References: <20141208100528.5f97106f@gandalf.local.home> X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.25; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 8 Dec 2014 10:05:28 -0500 Steven Rostedt wrote: > This code solves the issue of performing stack dumps from NMI context. > The issue is that printk() is not safe from NMI context as if the NMI > were to trigger when a printk() was being performed, the NMI could > deadlock from the printk() internal locks. This has been seen in practice. > One added bonus is that this code also makes the NMI dump stack work on PREEMPT_RT kernels. As printk() includes sleeping locks on PREEMPT_RT, printk() only writes to console if the console does not use any rt_mutex converted spin locks. Which a lot do. -- Steve