From: Qian Cai <cai@lca.pw>
To: Michal Hocko <mhocko@kernel.org>
Cc: David Hildenbrand <david@redhat.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
Andrew Morton <akpm@linux-foundation.org>,
Oscar Salvador <osalvador@suse.de>,
Pavel Tatashin <pasha.tatashin@soleen.com>,
Dan Williams <dan.j.williams@intel.com>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug_lock
Date: Thu, 26 Sep 2019 07:19:27 -0400 [thread overview]
Message-ID: <C8DA5249-2DEB-47D5-937E-5A774B1CB08B@lca.pw> (raw)
In-Reply-To: <20190926072645.GA20255@dhcp22.suse.cz>
> On Sep 26, 2019, at 3:26 AM, Michal Hocko <mhocko@kernel.org> wrote:
>
> OK, this is using for_each_online_cpu but why is this a problem? Have
> you checked what the code actually does? Let's say that online_pages is
> racing with cpu hotplug. A new CPU appears/disappears from the online
> mask while we are iterating it, right? Let's start with cpu offlining
> case. We have two choices, either the cpu is still visible and we update
> its local node configuration even though it will disappear shortly which
> is ok because we are not touching any data that disappears (it's all
> per-cpu). Case when the cpu is no longer there is not really
> interesting. For the online case we might miss a cpu but that should be
> tolerateable because that is not any different from triggering the
> online independently of the memory hotplug. So there has to be a hook
> from that code path as well. If there is none then this is buggy
> irrespective of the locking.
>
> Makes sense?
This sounds to me requires lots of audits and testing. Also, someone who is more
familiar with CPU hotplug should review this patch. Personally, I am no fun of
operating on an incorrect CPU mask to begin with, things could go wrong really
quickly...
next prev parent reply other threads:[~2019-09-26 11:19 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-24 14:36 [PATCH v1] mm/memory_hotplug: Don't take the cpu_hotplug_lock David Hildenbrand
2019-09-24 14:48 ` Michal Hocko
2019-09-24 15:01 ` David Hildenbrand
2019-09-24 15:03 ` Qian Cai
2019-09-24 15:11 ` Michal Hocko
2019-09-24 18:54 ` Qian Cai
2019-09-25 7:02 ` David Hildenbrand
2019-09-25 16:01 ` Qian Cai
2019-09-25 17:48 ` Michal Hocko
2019-09-25 18:20 ` Qian Cai
2019-09-25 19:48 ` David Hildenbrand
2019-09-25 20:32 ` Qian Cai
2019-09-26 7:26 ` David Hildenbrand
2019-09-26 7:38 ` Michal Hocko
2019-09-26 7:26 ` Michal Hocko
2019-09-26 11:19 ` Qian Cai [this message]
2019-09-26 11:52 ` Michal Hocko
2019-09-26 13:02 ` Qian Cai
2019-09-26 13:14 ` David Hildenbrand
2019-09-25 10:03 ` Michal Hocko
2019-09-24 15:23 ` David Hildenbrand
2019-10-02 21:37 ` Qian Cai
2019-10-04 7:42 ` David Hildenbrand
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