From: David Hildenbrand <david@redhat•com>
To: linux-mm@kvack•org
Cc: linux-kernel@vger•kernel.org, linux-doc@vger•kernel.org,
linuxppc-dev@lists•ozlabs.org, linux-acpi@vger•kernel.org,
xen-devel@lists•xenproject.org, devel@linuxdriverproject•org,
David Hildenbrand <david@redhat•com>,
Andrew Morton <akpm@linux-foundation•org>,
Balbir Singh <bsingharora@gmail•com>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Boris Ostrovsky <boris.ostrovsky@oracle•com>,
Dan Williams <dan.j.williams@intel•com>,
Greg Kroah-Hartman <gregkh@linuxfoundation•org>,
Haiyang Zhang <haiyangz@microsoft•com>,
Heiko Carstens <heiko.carstens@de•ibm.com>,
John Allen <jallen@linux•vnet.ibm.com>,
Jonathan Corbet <corbet@lwn•net>,
Joonsoo Kim <iamjoonsoo.kim@lge•com>,
Juergen Gross <jgross@suse•com>,
Kate Stewart <kstewart@linuxfoundation•org>,
"K. Y. Srinivasan" <kys@microsoft•com>,
Len Brown <lenb@kernel•org>,
Martin Schwidefsky <schwidefsky@de•ibm.com>,
Mathieu Malaterre <malat@debian•org>,
Michael Ellerman <mpe@ellerman•id.au>,
Michael Neuling <mikey@neuling•org>,
Michal Hocko <mhocko@suse•com>,
Nathan Fontenot <nfont@linux•vnet.ibm.com>,
Oscar Salvador <osalvador@suse•de>,
Paul Mackerras <paulus@samba•org>,
Pavel Tatashin <pasha.tatashin@oracle•com>,
Pavel Tatashin <pavel.tatashin@microsoft•com>,
Philippe Ombredanne <pombredanne@nexb•com>,
"Rafael J. Wysocki" <rjw@rjwysocki•net>,
Rashmica Gupta <rashmica.g@gmail•com>,
Stephen Hemminger <sthemmin@microsoft•com>,
Thomas Gleixner <tglx@linutronix•de>,
Vlastimil Babka <vbabka@suse•cz>,
YASUAKI ISHIMATSU <yasu.isimatu@gmail•com>
Subject: [PATCH v1 0/6] mm: online/offline_pages called w.o. mem_hotplug_lock
Date: Tue, 18 Sep 2018 13:48:16 +0200 [thread overview]
Message-ID: <20180918114822.21926-1-david@redhat.com> (raw)
Reading through the code and studying how mem_hotplug_lock is to be used,
I noticed that there are two places where we can end up calling
device_online()/device_offline() - online_pages()/offline_pages() without
the mem_hotplug_lock. And there are other places where we call
device_online()/device_offline() without the device_hotplug_lock.
While e.g.
echo "online" > /sys/devices/system/memory/memory9/state
is fine, e.g.
echo 1 > /sys/devices/system/memory/memory9/online
Will not take the mem_hotplug_lock. However the device_lock() and
device_hotplug_lock.
E.g. via memory_probe_store(), we can end up calling
add_memory()->online_pages() without the device_hotplug_lock. So we can
have concurrent callers in online_pages(). We e.g. touch in online_pages()
basically unprotected zone->present_pages then.
Looks like there is a longer history to that (see Patch #2 for details),
and fixing it to work the way it was intended is not really possible. We
would e.g. have to take the mem_hotplug_lock in device/base/core.c, which
sounds wrong.
Summary: We had a lock inversion on mem_hotplug_lock and device_lock().
More details can be found in patch 3 and patch 6.
I propose the general rules (documentation added in patch 6):
1. add_memory/add_memory_resource() must only be called with
device_hotplug_lock.
2. remove_memory() must only be called with device_hotplug_lock. This is
already documented and holds for all callers.
3. device_online()/device_offline() must only be called with
device_hotplug_lock. This is already documented and true for now in core
code. Other callers (related to memory hotplug) have to be fixed up.
4. mem_hotplug_lock is taken inside of add_memory/remove_memory/
online_pages/offline_pages.
To me, this looks way cleaner than what we have right now (and easier to
verify). And looking at the documentation of remove_memory, using
lock_device_hotplug also for add_memory() feels natural.
RFCv2 -> v1:
- Dropped an unnecessary _ref from remove_memory() in patch #1
- Minor patch description fixes.
- Added rb's
RFC -> RFCv2:
- Don't export device_hotplug_lock, provide proper remove_memory/add_memory
wrappers.
- Split up the patches a bit.
- Try to improve powernv memtrace locking
- Add some documentation for locking that matches my knowledge
David Hildenbrand (6):
mm/memory_hotplug: make remove_memory() take the device_hotplug_lock
mm/memory_hotplug: make add_memory() take the device_hotplug_lock
mm/memory_hotplug: fix online/offline_pages called w.o.
mem_hotplug_lock
powerpc/powernv: hold device_hotplug_lock when calling device_online()
powerpc/powernv: hold device_hotplug_lock in memtrace_offline_pages()
memory-hotplug.txt: Add some details about locking internals
Documentation/memory-hotplug.txt | 39 +++++++++++-
arch/powerpc/platforms/powernv/memtrace.c | 14 +++--
.../platforms/pseries/hotplug-memory.c | 8 +--
drivers/acpi/acpi_memhotplug.c | 4 +-
drivers/base/memory.c | 22 +++----
drivers/xen/balloon.c | 3 +
include/linux/memory_hotplug.h | 4 +-
mm/memory_hotplug.c | 59 +++++++++++++++----
8 files changed, 115 insertions(+), 38 deletions(-)
--
2.17.1
next reply other threads:[~2018-09-18 11:48 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-09-18 11:48 David Hildenbrand [this message]
2018-09-18 11:48 ` [PATCH v1 1/6] mm/memory_hotplug: make remove_memory() take the device_hotplug_lock David Hildenbrand
2018-09-18 21:18 ` Rafael J. Wysocki
2018-09-18 11:48 ` [PATCH v1 2/6] mm/memory_hotplug: make add_memory() " David Hildenbrand
2018-09-18 21:19 ` Rafael J. Wysocki
2018-09-18 11:48 ` [PATCH v1 3/6] mm/memory_hotplug: fix online/offline_pages called w.o. mem_hotplug_lock David Hildenbrand
2018-09-18 11:48 ` [PATCH v1 4/6] powerpc/powernv: hold device_hotplug_lock when calling device_online() David Hildenbrand
2018-09-18 11:48 ` [PATCH v1 5/6] powerpc/powernv: hold device_hotplug_lock in memtrace_offline_pages() David Hildenbrand
2018-09-18 11:48 ` [PATCH v1 6/6] memory-hotplug.txt: Add some details about locking internals David Hildenbrand
2018-09-19 1:22 ` [PATCH v1 0/6] mm: online/offline_pages called w.o. mem_hotplug_lock Balbir Singh
2018-09-19 7:35 ` David Hildenbrand
2018-09-23 2:34 ` Balbir Singh
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