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    Subject[PATCH V2 02/10] Drivers: hv: hv_balloon: keep locks balanced on add_memory() failure
    Date
    From: 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.

    The current char-next branch is broken and this patch fixes
    the bug.

    Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    Acked-by: Jason Wang <jasowang@redhat.com>
    Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
    ---
    drivers/hv/hv_balloon.c | 1 +
    1 files changed, 1 insertions(+), 0 deletions(-)

    diff --git a/drivers/hv/hv_balloon.c b/drivers/hv/hv_balloon.c
    index c5bb872..f1f17c5 100644
    --- a/drivers/hv/hv_balloon.c
    +++ b/drivers/hv/hv_balloon.c
    @@ -652,6 +652,7 @@ 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;
    }

    --
    1.7.4.1


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