drop_monitor: fix trace_napi_poll_hit()

The net_dev of backlog napi is NULL, like below:

__get_cpu_var(softnet_data).backlog.dev == NULL

So, we should check it in napi tracepoint's probe function

Acked-by: Neil Horman <nhorman@tuxdriver.com>
Signed-off-by: Xiao Guangrong <xiaoguangrong@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 2 insertions, 1 deletions

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 9d66fa953ab..d31120248c0 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -182,7 +182,8 @@ static void trace_napi_poll_hit(struct napi_struct *napi)
         /*
          * Ratelimit our check time to dm_hw_check_delta jiffies
          */
-        if (!time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
+        if (!napi->dev ||
+            !time_after(jiffies, napi->dev->last_rx + dm_hw_check_delta))
                 return;
 
         rcu_read_lock();