[Devel] [PATCH 09/12] drop_monitor: Reset per-CPU data before starting to trace

[Alexander Mikhalitsyn]

From: Ido Schimmel <idosch at mellanox.com>

The function reset_per_cpu_data() allocates and prepares a new skb for
the summary netlink alert message ('NET_DM_CMD_ALERT'). The new skb is
stored in the per-CPU 'data' variable and the old is returned.

The function is invoked during module initialization and from the
workqueue, before an alert is sent. This means that it is possible to
receive an alert with stale data, if we stopped tracing when the
hysteresis timer ('data->send_timer') was pending.

Instead of invoking the function during module initialization, invoke it
just before we start tracing and ensure we get a fresh skb.

This also allows us to remove the calls to initialize the timer and the
work item from the module initialization path, since both could have
been triggered by the error paths of reset_per_cpu_data().

Signed-off-by: Ido Schimmel <idosch at mellanox.com>
Signed-off-by: David S. Miller <davem at davemloft.net>
(cherry picked from commit 44075f563793880d17d1a2f3a17e06835b157d07)
---
 net/core/drop_monitor.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 41b558c58925..eaa1a0c7a028 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -248,9 +248,16 @@ static int net_dm_trace_on_set(void)
 
 	for_each_possible_cpu(cpu) {
 		struct per_cpu_dm_data *data = &per_cpu(dm_cpu_data, cpu);
+		struct sk_buff *skb;
 
 		INIT_WORK(&data->dm_alert_work, send_dm_alert);
 		timer_setup(&data->send_timer, sched_send_work, 0);
+		/* Allocate a new per-CPU skb for the summary alert message and
+		 * free the old one which might contain stale data from
+		 * previous tracing.
+		 */
+		skb = reset_per_cpu_data(data);
+		consume_skb(skb);
 	}
 
 	rc = register_trace_kfree_skb(trace_kfree_skb_hit, NULL);
@@ -463,10 +470,7 @@ static int __init init_net_drop_monitor(void)
 
 	for_each_possible_cpu(cpu) {
 		data = &per_cpu(dm_cpu_data, cpu);
-		INIT_WORK(&data->dm_alert_work, send_dm_alert);
-		timer_setup(&data->send_timer, sched_send_work, 0);
 		spin_lock_init(&data->lock);
-		reset_per_cpu_data(data);
 	}
 
 
-- 
2.36.1