linux-kernel - Re: possible deadlock in __wake_up_common

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Message-ID: <20190107213308.GE16284@hirez.programming.kicks-ass.net>
Date:   Mon, 7 Jan 2019 22:33:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        syzbot <syzbot+93d94a001cfbce9e60e1@...kaller.appspotmail.com>,
        aarcange@...hat.com, akpm@...ux-foundation.org,
        kirill.shutemov@...ux.intel.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linux@...inikbrodowski.net, mhocko@...e.com,
        rientjes@...gle.com, syzkaller-bugs@...glegroups.com,
        xieyisheng1@...wei.com, zhongjiang@...wei.com,
        Mel Gorman <mgorman@...hsingularity.net>,
        Ingo Molnar <mingo@...nel.org>
Subject: Re: possible deadlock in __wake_up_common_lock

On Mon, Jan 07, 2019 at 10:29:21PM +0100, Peter Zijlstra wrote:
> On Mon, Jan 07, 2019 at 03:46:27PM -0500, Johannes Weiner wrote:
> > Hm, so the splat says this:
> > 
> > wakeups take the pi lock
> > pi lock holders take the rq lock
> > rq lock holders take the timer base lock (thanks psi)
> > timer base lock holders take the zone lock (thanks kasan)

That's not kasan, that's debugobjects, and that would be equally true
for the hrtimer usage we already have in the scheduler.

With that, I'm not entirely sure we're responsible for this splat.. I'll
try and have another look tomorrow.