linux-kernel - Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 08 Oct 2019 09:06:29 -0400
From:   Qian Cai <cai@....pw>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Petr Mladek <pmladek@...e.com>, akpm@...ux-foundation.org,
        sergey.senozhatsky.work@...il.com, rostedt@...dmis.org,
        peterz@...radead.org, linux-mm@...ck.org,
        john.ogness@...utronix.de, david@...hat.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

On Tue, 2019-10-08 at 14:39 +0200, Michal Hocko wrote:
> On Tue 08-10-19 08:00:43, Qian Cai wrote:
> > 
> > 
> > > On Oct 8, 2019, at 6:39 AM, Michal Hocko <mhocko@...nel.org> wrote:
> > > 
> > > Have you actually triggered any real deadlock? With a zone->lock in
> > > place it would be pretty clear with hard lockups detected.
> > 
> > Yes, I did trigger here and there, and those lockdep splats are
> > especially useful to figure out why.
> 
> Can you provide a lockdep splat from an actual deadlock please? I am
> sorry but your responses tend to be really cryptic and I never know when
> you are talking about actual deadlocks and lockdep splats. I have asked
> about the former several times never receiving a specific answer.

It is very time-consuming to confirm a lockdep splat is 100% matching a deadlock
giving that it is not able to reproduce on will yet, so when I did encounter a
memory offline deadlock where "echo offline > memory/state" just hang, but there
is no hard lockup probably because the hard lockup detector did not work
properly for some reasons or it keep trying to acquire a spin lock that only
keep the CPU 100%.