From: Michal Hocko <mhocko@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: Baoquan He <bhe@redhat.com>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
akpm@linux-foundation.org, aarcange@redhat.com
Subject: Re: Memory hotplug softlock issue
Date: Wed, 14 Nov 2018 11:04:07 +0100 [thread overview]
Message-ID: <20181114100407.GL23419@dhcp22.suse.cz> (raw)
In-Reply-To: <9bb86c98-e062-b045-7c22-6f037bd56f36@redhat.com>
On Wed 14-11-18 10:48:09, David Hildenbrand wrote:
> On 14.11.18 10:41, Michal Hocko wrote:
> > On Wed 14-11-18 10:25:57, David Hildenbrand wrote:
> >> On 14.11.18 10:00, Baoquan He wrote:
> >>> Hi David,
> >>>
> >>> On 11/14/18 at 09:18am, David Hildenbrand wrote:
> >>>> Code seems to be waiting for the mem_hotplug_lock in read.
> >>>> We hold mem_hotplug_lock in write whenever we online/offline/add/remove
> >>>> memory. There are two ways to trigger offlining of memory:
> >>>>
> >>>> 1. Offlining via "cat offline > /sys/devices/system/memory/memory0/state"
> >>>>
> >>>> This always properly took the mem_hotplug_lock. Nothing changed
> >>>>
> >>>> 2. Offlining via "cat 0 > /sys/devices/system/memory/memory0/online"
> >>>>
> >>>> This didn't take the mem_hotplug_lock and I fixed that for this release.
> >>>>
> >>>> So if you were testing with 1., you should have seen the same error
> >>>> before this release (unless there is something else now broken in this
> >>>> release).
> >>>
> >>> Thanks a lot for looking into this.
> >>>
> >>> I triggered sysrq+t to check threads' state. You can see that we use
> >>> firmware to trigger ACPI event to go to acpi_bus_offline(), it truly
> >>> didn't take mem_hotplug_lock() and has taken it with your fix in
> >>> commit 381eab4a6ee mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock
> >>>
> >>> [ +0.007062] Workqueue: kacpi_hotplug acpi_hotplug_work_fn
> >>> [ +0.005398] Call Trace:
> >>> [ +0.002476] ? page_vma_mapped_walk+0x307/0x710
> >>> [ +0.004538] ? page_remove_rmap+0xa2/0x340
> >>> [ +0.004104] ? ptep_clear_flush+0x54/0x60
> >>> [ +0.004027] ? enqueue_entity+0x11c/0x620
> >>> [ +0.005904] ? schedule+0x28/0x80
> >>> [ +0.003336] ? rmap_walk_file+0xf9/0x270
> >>> [ +0.003940] ? try_to_unmap+0x9c/0xf0
> >>> [ +0.003695] ? migrate_pages+0x2b0/0xb90
> >>> [ +0.003959] ? try_offline_node+0x160/0x160
> >>> [ +0.004214] ? __offline_pages+0x6ce/0x8e0
> >>> [ +0.004134] ? memory_subsys_offline+0x40/0x60
> >>> [ +0.004474] ? device_offline+0x81/0xb0
> >>> [ +0.003867] ? acpi_bus_offline+0xdb/0x140
> >>> [ +0.004117] ? acpi_device_hotplug+0x21c/0x460
> >>> [ +0.004458] ? acpi_hotplug_work_fn+0x1a/0x30
> >>> [ +0.004372] ? process_one_work+0x1a1/0x3a0
> >>> [ +0.004195] ? worker_thread+0x30/0x380
> >>> [ +0.003851] ? drain_workqueue+0x120/0x120
> >>> [ +0.004117] ? kthread+0x112/0x130
> >>> [ +0.003411] ? kthread_park+0x80/0x80
> >>> [ +0.005325] ? ret_from_fork+0x35/0x40
> >>>
> >>
> >> Yes, this is indeed another code path that was fixed (and I didn't
> >> actually realize it ;) ). Thanks for the callchain. Before my fix
> >> hotplug still would have never succeeded (offline_pages would have
> >> silently looped forever) as far as I can tell.
> >
> > I haven't studied your patch yet so I am not really sure why you have
> > added the lock into this path. The memory hotplug locking is certainly
> > far from great but I believe we should really rething the scope of the
> > lock. There shouldn't be any fundamental reason to use the global lock
> > for the full offlining. So rather than moving the lock from one place to
> > another we need a range locking I believe.
> See the patches for details, the lock was removed on this path by
> mistake not by design.
OK, so I guess we should plug that hole first I guess.
> Replacing the lock by some range lock can now be done. The tricky part
> will be get_online_mems(), we'll have to indicate a range somehow. For
> online/offline/add/remove, we have the range.
I would argue that get_online_mems() needs some rethinking. Callers
shouldn't really care that a node went offline. If they care about the
specific pfn range of the node to not go away then the range locking
should work just fine for them.
--
Michal Hocko
SUSE Labs
next prev parent reply other threads:[~2018-11-14 10:04 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-14 7:09 Memory hotplug softlock issue Baoquan He
2018-11-14 7:16 ` Baoquan He
2018-11-14 8:18 ` David Hildenbrand
2018-11-14 9:00 ` Baoquan He
2018-11-14 9:25 ` David Hildenbrand
2018-11-14 9:41 ` Michal Hocko
2018-11-14 9:48 ` David Hildenbrand
2018-11-14 10:04 ` Michal Hocko [this message]
2018-11-14 9:01 ` Michal Hocko
2018-11-14 9:22 ` David Hildenbrand
2018-11-14 9:37 ` Michal Hocko
2018-11-14 9:39 ` David Hildenbrand
2018-11-14 14:52 ` Baoquan He
2018-11-14 15:00 ` Michal Hocko
2018-11-15 5:10 ` Baoquan He
2018-11-15 7:30 ` Michal Hocko
2018-11-15 7:53 ` Baoquan He
2018-11-15 8:30 ` Michal Hocko
2018-11-15 9:42 ` David Hildenbrand
2018-11-15 9:52 ` Baoquan He
2018-11-15 9:53 ` David Hildenbrand
2018-11-15 13:12 ` Baoquan He
2018-11-15 13:19 ` Michal Hocko
2018-11-15 13:23 ` Baoquan He
2018-11-15 14:25 ` Michal Hocko
2018-11-15 13:38 ` Baoquan He
2018-11-15 14:32 ` Michal Hocko
2018-11-15 14:34 ` Baoquan He
2018-11-16 1:24 ` Baoquan He
2018-11-16 9:14 ` Michal Hocko
2018-11-17 4:22 ` Baoquan He
[not found] ` <20181119105202.GE18471@MiWiFi-R3L-srv>
2018-11-19 12:40 ` Michal Hocko
2018-11-19 12:51 ` Michal Hocko
2018-11-19 14:10 ` Michal Hocko
2018-11-19 16:36 ` Vlastimil Babka
2018-11-19 16:46 ` Michal Hocko
2018-11-19 16:46 ` Vlastimil Babka
2018-11-19 16:48 ` Vlastimil Babka
2018-11-19 17:01 ` Michal Hocko
2018-11-19 17:33 ` Michal Hocko
2018-11-19 20:34 ` Hugh Dickins
2018-11-19 20:59 ` Michal Hocko
2018-11-20 1:56 ` Baoquan He
2018-11-20 5:44 ` Hugh Dickins
2018-11-20 13:38 ` Vlastimil Babka
2018-11-20 13:58 ` Baoquan He
2018-11-20 14:05 ` Michal Hocko
2018-11-20 14:12 ` Baoquan He
2018-11-21 1:21 ` Hugh Dickins
2018-11-21 1:08 ` Hugh Dickins
2018-11-21 3:20 ` Hugh Dickins
2018-11-21 17:31 ` Michal Hocko
2018-11-22 1:53 ` Hugh Dickins
2018-11-14 10:00 ` Michal Hocko
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