Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759064Ab3JOMyP (ORCPT ); Tue, 15 Oct 2013 08:54:15 -0400 Received: from mail-wi0-f178.google.com ([209.85.212.178]:55948 "EHLO mail-wi0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758762Ab3JOMyO (ORCPT ); Tue, 15 Oct 2013 08:54:14 -0400 Date: Tue, 15 Oct 2013 14:54:11 +0200 From: Frederic Weisbecker To: Peter Zijlstra Cc: "Liu, Chuansheng" , Steven Rostedt , "Ingo Molnar (mingo@kernel.org)" , "hpa@zytor.com" , "akpm@linux-foundation.org" , "paulmck@linux.vnet.ibm.com" , "x86@kernel.org" , "'linux-kernel@vger.kernel.org' (linux-kernel@vger.kernel.org)" , "Wang, Xiaoming" , "Li, Zhuangzhi" Subject: Re: Panic and page fault in loop during handling NMI backtrace handler Message-ID: <20131015125409.GB29884@localhost.localdomain> References: <27240C0AC20F114CBF8149A2696CBE4A01B60835@SHSMSX101.ccr.corp.intel.com> <20131015121849.GA29884@localhost.localdomain> <20131015123717.GJ10651@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131015123717.GJ10651@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1417 Lines: 26 On Tue, Oct 15, 2013 at 02:37:17PM +0200, Peter Zijlstra wrote: > On Tue, Oct 15, 2013 at 02:18:53PM +0200, Frederic Weisbecker wrote: > > On Tue, Oct 15, 2013 at 02:01:04AM +0000, Liu, Chuansheng wrote: > > > We meet one issue that during trigger all CPU backtrace, but during in the NMI handler arch_trigger_all_cpu_backtrace_handler, > > > It hit the PAGE fault, then PAGE fault is in loop, at last the thread stack overflow, and system panic. > > > > > > Anyone can give some help? Thanks. > > > > Looks like we re-enter the fault several times. On x86-32, NMIs can > > fault if they dereference vmalloc'ed area. I wonder if the module thing > > we lookup in the NMI is stored on some vmalloc'ed area. > > IIRC modules are indeed allocated using vmalloc. See module_alloc() > using vmalloc_exec() Right. At least the module text. Now I'm not sure the module_address_lookup() dereference that. But there many other objects allocated in module.c that use alloc_percpu(), which in turn can use vmalloc. IIRC Steve made the NMIs safely faultable. So may be we can remove the WARN_ON in do_page_fault(). It may not be a good idea to allow fault in NMIs though. Steve? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/