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| author | Vitaly Kuznetsov <vkuznets@redhat.com> | 2015-05-29 21:18:02 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2015-06-01 00:38:21 +0300 |
| commit | 4e4bd36f97b1492f19b3329ac74ed313da13de34 (patch) | |
| tree | 6768a2857429f56f4dc6833aa81fcd2c2a37c216 /drivers | |
| parent | 6c4e5f9c9ff41ea997fd0f345b3b2b88c113eb68 (diff) | |
| download | linux-4e4bd36f97b1492f19b3329ac74ed313da13de34.tar.xz | |
Drivers: hv: balloon: check if ha_region_mutex was acquired in MEM_CANCEL_ONLINE case
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>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/hv/hv_balloon.c | 4 |
1 files changed, 3 insertions, 1 deletions
diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c index cb5b7dc9797f..8a725cd69ad7 100644 --- a/drivers/hv/hv_balloon.c +++ b/drivers/hv/hv_balloon.c @@ -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); |