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Date: Tue, 7 Feb 2017 10:28:09 +0000
From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>, Dmitry Vyukov <dvyukov@google.com>,
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        Peter Zijlstra <peterz@infradead.org>,
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        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc
Message-ID: <20170207102809.awh22urqmfrav5r6@techsingularity.net>
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On Tue, Feb 07, 2017 at 10:49:28AM +0100, Vlastimil Babka wrote:
> On 02/07/2017 10:43 AM, Mel Gorman wrote:
> > If I'm reading this right, a hot-remove will set the pool POOL_DISASSOCIATED
> > and unbound. A workqueue queued for draining get migrated during hot-remove
> > and a drain operation will execute twice on a CPU -- one for what was
> > queued and a second time for the CPU it was migrated from. It should still
> > work with flush_work which doesn't appear to block forever if an item
> > got migrated to another workqueue. The actual drain workqueue function is
> > using the CPU ID it's currently running on so it shouldn't get confused.
> 
> Is the worker that will process this migrated workqueue also guaranteed
> to be pinned to a cpu for the whole work, though? drain_local_pages()
> needs that guarantee.
> 

It should be by running on a workqueue handler bound to that CPU (queued
on wq->cpu_pwqs in __queue_work)

-- 
Mel Gorman
SUSE Labs