Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933593AbbKMKrO (ORCPT ); Fri, 13 Nov 2015 05:47:14 -0500 Received: from mx2.suse.de ([195.135.220.15]:58239 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932758AbbKMKrJ (ORCPT ); Fri, 13 Nov 2015 05:47:09 -0500 Subject: Re: [PATCH V4] mm: fix kernel crash in khugepaged thread To: Steven Rostedt , yalin wang References: <1447316462-19645-1-git-send-email-yalin.wang2010@gmail.com> <20151112092923.19ee53dd@gandalf.local.home> Cc: mingo@redhat.com, akpm@linux-foundation.org, ebru.akagunduz@gmail.com, riel@redhat.com, kirill.shutemov@linux.intel.com, jmarchan@redhat.com, mgorman@techsingularity.net, willy@linux.intel.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org From: Vlastimil Babka Message-ID: <5645BFAA.1070004@suse.cz> Date: Fri, 13 Nov 2015 11:47:06 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 MIME-Version: 1.0 In-Reply-To: <20151112092923.19ee53dd@gandalf.local.home> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2361 Lines: 67 On 11/12/2015 03:29 PM, Steven Rostedt wrote: > On Thu, 12 Nov 2015 16:21:02 +0800 > yalin wang wrote: > >> This crash is caused by NULL pointer deference, in page_to_pfn() marco, >> when page == NULL : >> >> [ 182.639154 ] Unable to handle kernel NULL pointer dereference at virtual address 00000000 > > >> add the trace point with TP_CONDITION(page), > > I wonder if we still want to trace even if page is NULL? I'd say we want to. There's even a "SCAN_PAGE_NULL" result defined for that case, and otherwise we would only have to guess why collapsing failed, which is the thing that the tracepoint should help us find out in the first place :) >> avoid trace NULL page. >> >> Signed-off-by: yalin wang >> --- >> include/trace/events/huge_memory.h | 20 ++++++++++++-------- >> mm/huge_memory.c | 6 +++--- >> 2 files changed, 15 insertions(+), 11 deletions(-) >> >> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h >> index 11c59ca..727647b 100644 >> --- a/include/trace/events/huge_memory.h >> +++ b/include/trace/events/huge_memory.h >> @@ -45,12 +45,14 @@ SCAN_STATUS >> #define EM(a, b) {a, b}, >> #define EMe(a, b) {a, b} >> >> -TRACE_EVENT(mm_khugepaged_scan_pmd, >> +TRACE_EVENT_CONDITION(mm_khugepaged_scan_pmd, >> >> - TP_PROTO(struct mm_struct *mm, unsigned long pfn, bool writable, >> + TP_PROTO(struct mm_struct *mm, struct page *page, bool writable, >> bool referenced, int none_or_zero, int status, int unmapped), >> >> - TP_ARGS(mm, pfn, writable, referenced, none_or_zero, status, unmapped), >> + TP_ARGS(mm, page, writable, referenced, none_or_zero, status, unmapped), >> + >> + TP_CONDITION(page), >> >> TP_STRUCT__entry( >> __field(struct mm_struct *, mm) >> @@ -64,7 +66,7 @@ TRACE_EVENT(mm_khugepaged_scan_pmd, >> >> TP_fast_assign( >> __entry->mm = mm; >> - __entry->pfn = pfn; >> + __entry->pfn = page_to_pfn(page); > > Instead of the condition, we could have: > > __entry->pfn = page ? page_to_pfn(page) : -1; I agree. Please do it like this. -- 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/