[PATCH] Drivers: hv: hv_balloon: keep locks balanced on add_memory() failure

[Vitaly Kuznetsov <vkuznets@redhat.com>]

When add_memory() fails the following BUG is observed:
[  743.646107] hv_balloon: hot_add memory failed error is -17
[  743.679973]
[  743.680930] =====================================
[  743.680930] [ BUG: bad unlock balance detected! ]
[  743.680930] 3.19.0-rc5_bug1131426+ #552 Not tainted
[  743.680930] -------------------------------------
[  743.680930] kworker/0:2/255 is trying to release lock (&dm_device.ha_region_mutex) at:
[  743.680930] [<ffffffff81aae5fe>] mutex_unlock+0xe/0x10
[  743.680930] but there are no more locks to release!

This happens as we don't acquire ha_region_mutex and hot_add_req() expects us
to as it does unconditional mutex_unlock(). Acquire the lock on the error path.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
This patch is dependent on the previously posted 'Drivers: hv: hv_balloon:
eliminate the trylock path in acquire/release_region_mutex'.
---
 drivers/hv/hv_balloon.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
index 1283035..771bf84 100644
--- a/drivers/hv/hv_balloon.c
+++ b/drivers/hv/hv_balloon.c
@@ -654,6 +654,7 @@ static void hv_mem_hot_add(unsigned long start, unsigned long size,
 			}
 			has->ha_end_pfn -= HA_CHUNK;
 			has->covered_end_pfn -=  processed_pfn;
+			mutex_lock(&dm_device.ha_region_mutex);
 			break;
 		}
 
-- 
1.9.3