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Date: Tue, 7 Feb 2017 09:46:13 +0000
From: Mel Gorman <mgorman@techsingularity.net>
To: Vlastimil Babka <vbabka@suse.cz>
Cc: Michal Hocko <mhocko@kernel.org>, Dmitry Vyukov <dvyukov@google.com>,
        Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
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        Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        syzkaller <syzkaller@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>
Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc
Message-ID: <20170207094613.svdhedw6u6cuvgif@techsingularity.net>
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On Tue, Feb 07, 2017 at 10:23:31AM +0100, Vlastimil Babka wrote:
> 
> > cpu offlining. I have to check the code but my impression was that WQ
> > code will ignore the cpu requested by the work item when the cpu is
> > going offline. If the offline happens while the worker function already
> > executes then it has to wait as we run with preemption disabled so we
> > should be safe here. Or am I missing something obvious?
> 
> Tejun suggested an alternative solution to avoiding get_online_cpus() in
> this thread:
> https://lkml.kernel.org/r/<20170123170329.GA7820@htj.duckdns.org>

I was hoping it would not really be necessary to sync against the cpu
offline callback if we know we don't really have to guarantee we run on
the correct CPU.

-- 
Mel Gorman
SUSE Labs