From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f71.google.com (mail-pg0-f71.google.com [74.125.83.71]) by kanga.kvack.org (Postfix) with ESMTP id 7B0786B025E for ; Wed, 1 Nov 2017 08:01:13 -0400 (EDT) Received: by mail-pg0-f71.google.com with SMTP id 15so2347968pgc.16 for ; Wed, 01 Nov 2017 05:01:13 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [65.50.211.133]) by mx.google.com with ESMTPS id q81si726792pfi.503.2017.11.01.05.01.11 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 01 Nov 2017 05:01:12 -0700 (PDT) Date: Wed, 1 Nov 2017 13:01:01 +0100 From: Peter Zijlstra Subject: Re: possible deadlock in lru_add_drain_all Message-ID: <20171101120101.d6jlzwjks2j3az2v@hirez.programming.kicks-ass.net> References: <20171030082203.4xvq2af25shfci2z@dhcp22.suse.cz> <20171030100921.GA18085@X58A-UD3R> <20171030151009.ip4k7nwan7muouca@hirez.programming.kicks-ass.net> <20171031131333.pr2ophwd2bsvxc3l@dhcp22.suse.cz> <20171031135104.rnlytzawi2xzuih3@hirez.programming.kicks-ass.net> <20171031145247.5kjbanjqged34lbp@hirez.programming.kicks-ass.net> <20171031145804.ulrpk245ih6t7q7h@dhcp22.suse.cz> <20171031151024.uhbaynabzq6k7fbc@hirez.programming.kicks-ass.net> <20171101085927.GB3172@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171101085927.GB3172@X58A-UD3R> Sender: owner-linux-mm@kvack.org List-ID: To: Byungchul Park Cc: Michal Hocko , Dmitry Vyukov , syzbot , Andrew Morton , Dan Williams , Johannes Weiner , Jan Kara , jglisse@redhat.com, LKML , linux-mm@kvack.org, shli@fb.com, syzkaller-bugs@googlegroups.com, Thomas Gleixner , Vlastimil Babka , ying.huang@intel.com, kernel-team@lge.com On Wed, Nov 01, 2017 at 05:59:27PM +0900, Byungchul Park wrote: > On Tue, Oct 31, 2017 at 04:10:24PM +0100, Peter Zijlstra wrote: > > On Tue, Oct 31, 2017 at 03:58:04PM +0100, Michal Hocko wrote: > > > On Tue 31-10-17 15:52:47, Peter Zijlstra wrote: > > > [...] > > > > If we want to save those stacks; we have to save a stacktrace on _every_ > > > > lock acquire, simply because we never know ahead of time if there will > > > > be a new link. Doing this is _expensive_. > > > > > > > > Furthermore, the space into which we store stacktraces is limited; > > > > since memory allocators use locks we can't very well use dynamic memory > > > > for lockdep -- that would give recursive and robustness issues. > > I agree with all you said. > > But, I have a better idea, that is, to save only the caller's ip of each > acquisition as an additional information? Of course, it's not enough in > some cases, but it's cheep and better than doing nothing. > > For example, when building A->B, let's save not only full stack of B, > but also caller's ip of A together, then use them on warning like: Like said; I've never really had trouble finding where we take A. And for the most difficult cases, just the IP isn't too useful either. So that would solve a non problem while leaving the real problem. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org