linux-kernel - Re: v4.16+ seeing many unaligned access in dequeue_task

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Message-ID: <20180403185829.yteixqsb5zazmav6@agluck-desk>
Date:   Tue, 3 Apr 2018 11:58:34 -0700
From:   "Luck, Tony" <tony.luck@...el.com>
To:     Patrick Bellasi <patrick.bellasi@....com>
Cc:     Mel Gorman <mgorman@...hsingularity.net>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>,
        Norbert Manthey <nmanthey@...zon.de>,
        Frederic Weisbecker <frederic@...nel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: v4.16+ seeing many unaligned access in dequeue_task_fair() on
 IA64

On Tue, Apr 03, 2018 at 09:37:06AM +0200, Peter Zijlstra wrote:
> On Mon, Apr 02, 2018 at 04:24:49PM -0700, Luck, Tony wrote:
> > Any guesses before I start to bisect?
> 
> That doesn't sound good. The only guess I have at this moment is you
> accidentially enabled RANDSTRUCT_PLUGIN and that messes things up.
> 
> struct task_struct whould be at least L1_CACHE_BYTES aligned, and C
> otherwise makes it fairly hard to cause unaligned accesses. Packed
> structures and/or casting are required, and I don't think we added
> anything dodgy like that here.

bisect says:

d519329f72a6 ("sched/fair: Update util_est only on util_avg updates")

Reverting just this commit makes the problem go away.

-Tony