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Date: Thu, 2 Nov 2017 08:54:56 +0900 From: Byungchul Park <byungchul.park@....com> To: Peter Zijlstra <peterz@...radead.org> Cc: Michal Hocko <mhocko@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>, syzbot <bot+e7353c7141ff7cbb718e4c888a14fa92de41ebaa@...kaller.appspotmail.com>, Andrew Morton <akpm@...ux-foundation.org>, Dan Williams <dan.j.williams@...el.com>, Johannes Weiner <hannes@...xchg.org>, Jan Kara <jack@...e.cz>, jglisse@...hat.com, LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org, shli@...com, syzkaller-bugs@...glegroups.com, Thomas Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>, ying.huang@...el.com, kernel-team@....com Subject: Re: possible deadlock in lru_add_drain_all On Wed, Nov 01, 2017 at 01:01:01PM +0100, Peter Zijlstra wrote: > 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 Me, either, since I know the way. But I've seen many guys who got confused with it, which is why I suggested it. But, leave it if you don't think so. > 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.
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