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From: Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH] sched: Relax a restriction in sched_rt_can_attach()
Date: Tue, 5 May 2015 21:00:57 +0200
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To: Tejun Heo <tj@kernel.org>
Cc: Zefan Li <lizefan@huawei.com>, Mike Galbraith <umgwanakikbuti@gmail.com>, Ingo Molnar <mingo@kernel.org>, LKML <linux-kernel@vger.kernel.org>, Cgroups <cgroups@vger.kernel.org>

On Tue, May 05, 2015 at 12:31:12PM -0400, Tejun Heo wrote:
> 
> What I don't want to happen is controllers failing migrations
> willy-nilly for random reasons leaving users baffled, which we've
> actually been doing unfortunately.  Maybe we need to deal with this
> fixed resource arbitration as a separate class and allow them to fail
> migration w/ -EBUSY.

Ah, _that_ was the problem.

Which is something created by this co-mounting of controllers.

You could of course store the ss-id of the failing operation in
task_struct and have a file reporting the name of the ss-id.

That way, there is a simple way to find out which controller failed the
migrate.