Date:	Thu, 12 Feb 2015 15:38:42 +0000
From:	KY Srinivasan <kys@...rosoft.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Yasuaki Ishimatsu" <isimatu.yasuaki@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	David Rientjes <rientjes@...gle.com>,
	Fabian Frederick <fabf@...net.be>,
	Zhang Zhen <zhenzhang.zhang@...wei.com>,
	Vladimir Davydov <vdavydov@...allels.com>,
	"Wang Nan" <wangnan0@...wei.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: RE: [PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock between
 memory adding and onlining



> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@...hat.com]
> Sent: Thursday, February 12, 2015 2:24 AM
> To: linux-kernel@...r.kernel.org
> Cc: Greg Kroah-Hartman; KY Srinivasan; Haiyang Zhang; Andrew Morton;
> Yasuaki Ishimatsu; Tang Chen; Vlastimil Babka; David Rientjes; Fabian
> Frederick; Zhang Zhen; Vladimir Davydov; Wang Nan; Rafael J. Wysocki;
> devel@...uxdriverproject.org; linux-mm@...ck.org
> Subject: [PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock
> between memory adding and onlining
> 
> RESEND (with no changes) because Rafael J. Wysocki was missing in
> recepients.
> 
> If newly added memory is brought online with e.g. udev rule:
> SUBSYSTEM=="memory", ACTION=="add", ATTR{state}="online"
> the following deadlock is observed (and easily reproducable):
> 
> First participant, worker thread doing add_memory():
> 
> [  724.948846] kworker/0:1     D ffff88000412f9c8 13248    27      2 0x00000000
> [  724.973543] Workqueue: events hot_add_req [hv_balloon] [  724.991736]
> ffff88000412f9c8 0000000000000000 ffff88003fa1dc30 00000000000151c0 [
> 725.019725]  0000000000000246 ffff88000412ffd8 00000000000151c0
> ffff88003a77a4e0 [  725.046486]  ffff88003fa1dc30 00000001032a6000
> ffff88003a7ca838 ffff88003a7ca898 [  725.072969] Call Trace:
> [  725.082690]  [<ffffffff81aac0a9>] schedule_preempt_disabled+0x29/0x70
> [  725.103799]  [<ffffffff81aae33b>] mutex_lock_nested+0x14b/0x470 [
> 725.122367]  [<ffffffff815ed773>] ? device_attach+0x23/0xb0 [  725.140992]
> [<ffffffff815ed773>] device_attach+0x23/0xb0 [  725.159131]
> [<ffffffff815ecba0>] bus_probe_device+0xb0/0xe0 [  725.177055]
> [<ffffffff815ea693>] device_add+0x443/0x650 [  725.195558]
> [<ffffffff815ea8be>] device_register+0x1e/0x30 [  725.213133]
> [<ffffffff81601790>] init_memory_block+0xd0/0xf0 [  725.231533]
> [<ffffffff816018f1>] register_new_memory+0xb1/0xd0 [  725.250769]
> [<ffffffff81a961cf>] __add_pages+0x13f/0x250 [  725.269642]
> [<ffffffff81063770>] ? arch_add_memory+0x70/0xf0 [  725.288764]
> [<ffffffff81063770>] arch_add_memory+0x70/0xf0 [  725.306117]
> [<ffffffff81a95f8f>] add_memory+0xef/0x1f0 [  725.322466]
> [<ffffffffa00293af>] hot_add_req+0x33f/0xf90 [hv_balloon] [  725.342777]
> [<ffffffff8109509f>] process_one_work+0x1df/0x4e0 [  725.361459]
> [<ffffffff8109502d>] ? process_one_work+0x16d/0x4e0 [  725.380390]
> [<ffffffff810954bb>] worker_thread+0x11b/0x450 [  725.397684]
> [<ffffffff810953a0>] ? process_one_work+0x4e0/0x4e0 [  725.416533]
> [<ffffffff8109ac33>] kthread+0xf3/0x110 [  725.433372]  [<ffffffff8109ab40>]
> ? kthread_create_on_node+0x240/0x240
> [  725.453749]  [<ffffffff81ab1dfc>] ret_from_fork+0x7c/0xb0 [  725.470994]
> [<ffffffff8109ab40>] ? kthread_create_on_node+0x240/0x240
> [  725.491469] 6 locks held by kworker/0:1/27:
> [  725.505037]  #0:  ("events"){......}, at: [<ffffffff8109502d>]
> process_one_work+0x16d/0x4e0 [  725.533370]  #1:
> ((&dm_device.ha_wrk.wrk)){......}, at: [<ffffffff8109502d>]
> process_one_work+0x16d/0x4e0 [  725.565580]  #2:
> (mem_hotplug.lock){......}, at: [<ffffffff811e6525>]
> mem_hotplug_begin+0x5/0x80 [  725.594369]  #3:
> (mem_hotplug.lock#2){......}, at: [<ffffffff811e656f>]
> mem_hotplug_begin+0x4f/0x80 [  725.628554]  #4:
> (mem_sysfs_mutex){......}, at: [<ffffffff81601873>]
> register_new_memory+0x33/0xd0 [  725.658519]  #5:  (&dev->mutex){......},
> at: [<ffffffff815ed773>] device_attach+0x23/0xb0
> 
> Second participant, udev:
> 
> [  725.750889] systemd-udevd   D ffff88003b94fc68 14016   888    530
> 0x00000004
> [  725.773767]  ffff88003b94fc68 0000000000000000 ffff8800034949c0
> 00000000000151c0 [  725.798332]  ffffffff8210d980 ffff88003b94ffd8
> 00000000000151c0 ffff880037a69270 [  725.822841]  ffff8800034949c0
> 0000000100000001 ffff8800034949c0 ffffffff81ff2b48 [  725.849184] Call Trace:
> [  725.858987]  [<ffffffff81aac0a9>] schedule_preempt_disabled+0x29/0x70
> [  725.879231]  [<ffffffff81aae33b>] mutex_lock_nested+0x14b/0x470 [
> 725.897860]  [<ffffffff811e656f>] ? mem_hotplug_begin+0x4f/0x80 [
> 725.916698]  [<ffffffff811e656f>] mem_hotplug_begin+0x4f/0x80 [
> 725.935064]  [<ffffffff811e6525>] ? mem_hotplug_begin+0x5/0x80 [
> 725.953464]  [<ffffffff81a9631b>] online_pages+0x3b/0x520 [  725.971542]
> [<ffffffff815eb0b3>] ? device_online+0x23/0xa0 [  725.989207]
> [<ffffffff81601524>] memory_subsys_online+0x64/0xc0 [  726.008513]
> [<ffffffff815eb0fd>] device_online+0x6d/0xa0 [  726.025579]
> [<ffffffff816012eb>] store_mem_state+0x5b/0xe0 [  726.043400]
> [<ffffffff815e8258>] dev_attr_store+0x18/0x30 [  726.060506]
> [<ffffffff8127a808>] sysfs_kf_write+0x48/0x60 [  726.077940]
> [<ffffffff81279d1b>] kernfs_fop_write+0x13b/0x1a0 [  726.099416]
> [<ffffffff811f9f67>] vfs_write+0xb7/0x1f0 [  726.115748]  [<ffffffff811fabf8>]
> SyS_write+0x58/0xd0 [  726.131933]  [<ffffffff81ab1ea9>]
> system_call_fastpath+0x12/0x17 [  726.150691] 7 locks held by systemd-
> udevd/888:
> [  726.165044]  #0:  (sb_writers#3){......}, at: [<ffffffff811fa063>]
> vfs_write+0x1b3/0x1f0 [  726.192422]  #1:  (&of->mutex){......}, at:
> [<ffffffff81279c46>] kernfs_fop_write+0x66/0x1a0 [  726.220289]  #2:
> (s_active#60){......}, at: [<ffffffff81279c4e>] kernfs_fop_write+0x6e/0x1a0 [
> 726.249382]  #3:  (device_hotplug_lock){......}, at: [<ffffffff815e9c15>]
> lock_device_hotplug_sysfs+0x15/0x50
> [  726.281901]  #4:  (&dev->mutex){......}, at: [<ffffffff815eb0b3>]
> device_online+0x23/0xa0 [  726.308619]  #5:  (mem_hotplug.lock){......}, at:
> [<ffffffff811e6525>] mem_hotplug_begin+0x5/0x80 [  726.337994]  #6:
> (mem_hotplug.lock#2){......}, at: [<ffffffff811e656f>]
> mem_hotplug_begin+0x4f/0x80
> 
> In short: onlining grabs device lock and then tries to do
> mem_hotplug_begin() while add_memory() is between
> mem_hotplug_begin() and mem_hotplug_done() and it tries grabbing
> device lock.
> 
> To my understanding ACPI memory hotplug doesn't have the same issue as
> device_hotplug_lock is being grabbed when the ACPI device is added.
> 
> Solve the issue by grabbing device_hotplug_lock before doing
> add_memory(). If we do that, lock_device_hotplug_sysfs() will cause syscall
> retry which will eventually succeed. To support the change we need to
> export lock_device_hotplug/ unlock_device_hotplug. This approach can be
> completely wrong though.

This issue was first discovered by Andy Whitcroft: https://lkml.org/lkml/2014/3/14/451
I had sent patches based on Andy's analysis that did not affect the users of the kernel hot-add
memory APIs: https://lkml.org/lkml/2014/12/2/662

This patch puts the burden where it needs to be and can address the issue for all clients.

K. Y
> 
> Vitaly Kuznetsov (3):
>   driver core: export lock_device_hotplug/unlock_device_hotplug
>   memory_hotplug: add note about holding device_hotplug_lock and
>     add_memory()
>   Drivers: hv: balloon: fix deadlock between memory adding and onlining
> 
>  drivers/base/core.c     |  2 ++
>  drivers/hv/hv_balloon.c | 10 ++++++++++
>  mm/memory_hotplug.c     |  6 +++++-
>  3 files changed, 17 insertions(+), 1 deletion(-)
> 
> --
> 1.9.3

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