[PATCH resend] drop_monitor: fix trace_napi_poll_hit()

[Xiao Guangrong]

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@xxxxxxxxxxxxx>
Signed-off-by: Xiao Guangrong <xiaoguangrong@xxxxxxxxxxxxxx>
---
 net/core/drop_monitor.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 9d66fa9..d311202 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();
-- 
1.6.1.2

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