From 4e4bd36f97b1492f19b3329ac74ed313da13de34 Mon Sep 17 00:00:00 2001 From: Vitaly Kuznetsov Date: Fri, 29 May 2015 11:18:02 -0700 Subject: [PATCH] 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] [] 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 Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman --- drivers/hv/hv_balloon.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) 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);