linux-kernel - Re: possible deadlock in lru_add_drain

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Message-ID: <20171031152532.uah32qiftjerc3gx@hirez.programming.kicks-ass.net>
Date:   Tue, 31 Oct 2017 16:25:32 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     Byungchul Park <byungchul.park@....com>,
        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 Tue, Oct 31, 2017 at 02:13:33PM +0100, Michal Hocko wrote:

> > I can indeed confirm it's running old code; cpuhp_state is no more.
> 
> Does this mean the below chain is no longer possible with the current
> linux-next (tip)?

I see I failed to answer this; no it will happen but now reads like:

	s/cpuhp_state/&_up/

Where we used to have a single lock protecting the hotplug stuff, we now
have 2, one for bringing stuff up and one for tearing it down.

This got rid of lock cycles that included cpu-up and cpu-down parts;
those are false positives because we cannot do cpu-up and cpu-down
concurrently.

But this report only includes a single (cpu-up) part and therefore is
not affected by that change other than a lock name changing.