Re: v4.16+ seeing many unaligned access in dequeue_task_fair() on IA64

[Luck, Tony]

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