From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754336AbcHSOHs (ORCPT ); Fri, 19 Aug 2016 10:07:48 -0400 Received: from outbound-smtp03.blacknight.com ([81.17.249.16]:44939 "EHLO outbound-smtp03.blacknight.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753995AbcHSOHr (ORCPT ); Fri, 19 Aug 2016 10:07:47 -0400 Date: Fri, 19 Aug 2016 15:00:26 +0100 From: Mel Gorman To: Pankaj Gupta Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, akpm@linux-foundation.org, vbabka@suse.cz, riel@redhat.com, hannes@cmpxchg.org, iamjoonsoo kim , kirill shutemov , izumi taku Subject: Re: [PATCH] mm: Add WARN_ON for possibility of infinite loop if empty lists in free_pcppages_bulk' Message-ID: <20160819140026.GN8119@techsingularity.net> References: <1471608918-5101-1-git-send-email-pagupta@redhat.com> <20160819124508.GM8119@techsingularity.net> <945408416.2306040.1471612041111.JavaMail.zimbra@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <945408416.2306040.1471612041111.JavaMail.zimbra@redhat.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 19, 2016 at 09:07:21AM -0400, Pankaj Gupta wrote: > > > > > On Fri, Aug 19, 2016 at 05:45:18PM +0530, Pankaj Gupta wrote: > > > While debugging issue in realtime kernel i found a scenario > > > which resulted in infinite loop resulting because of empty pcp->lists > > > and valid 'to_free' value. This patch is to add 'WARN_ON' in function > > > 'free_pcppages_bulk' if there is possibility of infinite loop because > > > of any bug in code. > > > > > > > What was the bug that allowed this situation to occur? It would imply > > the pcp count was somehow out of sync. > > Yes pcp count was out of sync. It was a bug in the downstream code. If the bug is not in the mainline code, I think it would be inappropriate to add unnecessary code to a relatively hot path. At most, it should be a VM_BUG_ON but the soft lockup should be clear enough. -- Mel Gorman SUSE Labs