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Drivers: hv: balloon: check if ha_region_mutex was acquired in MEM_CANCEL_ONLINE case

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Memory notifiers are being executed in a sequential order and when one of
them fails returning something different from NOTIFY_OK the remainder of
the notification chain is not being executed. When a memory block is being
onlined in online_pages() we do memory_notify(MEM_GOING_ONLINE, ) and if
one of the notifiers in the chain fails we end up doing
memory_notify(MEM_CANCEL_ONLINE, ) so it is possible for a notifier to see
MEM_CANCEL_ONLINE without seeing the corresponding MEM_GOING_ONLINE event.
E.g. when CONFIG_KASAN is enabled the kasan_mem_notifier() is being used
to prevent memory hotplug, it returns NOTIFY_BAD for all MEM_GOING_ONLINE
events. As kasan_mem_notifier() comes before the hv_memory_notifier() in
the notification chain we don't see the MEM_GOING_ONLINE event and we do
not take the ha_region_mutex. We, however, see the MEM_CANCEL_ONLINE event
and unconditionally try to release the lock, the following is observed:

[  110.850927] =====================================
[  110.850927] [ BUG: bad unlock balance detected! ]
[  110.850927] 4.1.0-rc3_bugxxxxxxx_test_xxxx #595 Not tainted
[  110.850927] -------------------------------------
[  110.850927] systemd-udevd/920 is trying to release lock
(&dm_device.ha_region_mutex) at:
[  110.850927] [<ffffffff81acda0e>] mutex_unlock+0xe/0x10
[  110.850927] but there are no more locks to release!

At the same time we can have the ha_region_mutex taken when we get the
MEM_CANCEL_ONLINE event in case one of the memory notifiers after the
hv_memory_notifier() in the notification chain failed so we need to add
the mutex_is_locked() check. In case of MEM_ONLINE we are always supposed
to have the mutex locked.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Vitaly Kuznetsov 2015-05-29 11:18:02 -07:00 committed by Greg Kroah-Hartman
parent 6c4e5f9c9f
commit 4e4bd36f97
1 changed files with 3 additions and 1 deletions
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4
drivers/hv/hv_balloon.c
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@ -567,7 +567,9 @@ static int hv_memory_notifier(struct notifier_block *nb, unsigned long val,
case MEM_ONLINE:
dm_device.num_pages_onlined += mem->nr_pages;
case MEM_CANCEL_ONLINE:
mutex_unlock(&dm_device.ha_region_mutex);
if (val == MEM_ONLINE ||
mutex_is_locked(&dm_device.ha_region_mutex))
mutex_unlock(&dm_device.ha_region_mutex);
if (dm_device.ha_waiting) {
dm_device.ha_waiting = false;
complete(&dm_device.ol_waitevent);