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

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Message-ID: <20191008191728.GS6681@dhcp22.suse.cz>
Date:   Tue, 8 Oct 2019 21:17:28 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Qian Cai <cai@....pw>
Cc:     Christian Borntraeger <borntraeger@...ibm.com>,
        Petr Mladek <pmladek@...e.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.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,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>
Subject: Re: [PATCH v2] mm/page_isolation: fix a deadlock with printk()

On Tue 08-10-19 15:06:13, Qian Cai wrote:
> On Tue, 2019-10-08 at 20:35 +0200, Michal Hocko wrote:
[...]
> > I fully agree that this class of lockdep splats are annoying especially
> > when they make the lockdep unusable but please discuss this with lockdep
> > maintainers and try to find some solution rather than go and try to
> > workaround the problem all over the place. If there are places that
> > would result in a cleaner code then go for it but please do not make the
> > code worse just because of a non existent problem flagged by a false
> > positive.
> 
> It makes me wonder what make you think it is a false positive for sure.

Because this is an early init code? Because if it were a real deadlock
then your system wouldn't boot to get run with the real userspace
(remember there is zone->lock spinlock involved and that means that you
would hit hard lock after few seconds - but I feel I am repeating
myself).
-- 
Michal Hocko
SUSE Labs