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Date: Wed, 8 Feb 2017 09:06:47 -0600 (CST)
From: Christoph Lameter <cl@linux.com>
Subject: Re: mm: deadlock between get_online_cpus/pcpu_alloc
In-Reply-To: <alpine.DEB.2.20.1702072319200.8117@nanos>
Message-ID: <alpine.DEB.2.20.1702080906100.3955@east.gentwo.org>
References: <2cdef192-1939-d692-1224-8ff7d7ff7203@suse.cz> <20170207102809.awh22urqmfrav5r6@techsingularity.net> <20170207103552.GH5065@dhcp22.suse.cz> <20170207113435.6xthczxt2cx23r4t@techsingularity.net> <20170207114327.GI5065@dhcp22.suse.cz>
 <20170207123708.GO5065@dhcp22.suse.cz> <20170207135846.usfrn7e4znjhmogn@techsingularity.net> <20170207141911.GR5065@dhcp22.suse.cz> <20170207153459.GV5065@dhcp22.suse.cz> <20170207162224.elnrlgibjegswsgn@techsingularity.net> <20170207164130.GY5065@dhcp22.suse.cz>
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Sender: owner-linux-mm@kvack.org
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To: Thomas Gleixner <tglx@linutronix.de>
Cc: Michal Hocko <mhocko@kernel.org>, Mel Gorman <mgorman@techsingularity.net>, Vlastimil Babka <vbabka@suse.cz>, Dmitry Vyukov <dvyukov@google.com>, Tejun Heo <tj@kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, LKML <linux-kernel@vger.kernel.org>, Ingo Molnar <mingo@kernel.org>, Peter Zijlstra <peterz@infradead.org>, syzkaller <syzkaller@googlegroups.com>, Andrew Morton <akpm@linux-foundation.org>

On Tue, 7 Feb 2017, Thomas Gleixner wrote:

> > Yep. Hotplug events are pretty significant. Using stop_machine_XXXX() etc
> > would be advisable and that would avoid the taking of locks and get rid of all the
> > ocmplexity, reduce the code size and make the overall system much more
> > reliable.
>
> Huch? stop_machine() is horrible and heavy weight. Don't go there, there
> must be simpler solutions than that.

Inserting or removing hardware is a heavy process. This would help quite a
bit with these issues for loops over active cpus.

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