[PATCH RESEND 0/3] memory_hotplug: hyperv: fix deadlock between memory adding and onlining

[Vitaly Kuznetsov]

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.

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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