netdev - [RFC PATCH net-next 03/12] drop_monitor: Document scope of spinlock

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Date:   Mon, 22 Jul 2019 21:31:25 +0300
From:   Ido Schimmel <idosch@...sch.org>
To:     netdev@...r.kernel.org
Cc:     davem@...emloft.net, nhorman@...driver.com, dsahern@...il.com,
        roopa@...ulusnetworks.com, nikolay@...ulusnetworks.com,
        jakub.kicinski@...ronome.com, toke@...hat.com, andy@...yhouse.net,
        f.fainelli@...il.com, andrew@...n.ch, vivien.didelot@...il.com,
        mlxsw@...lanox.com, Ido Schimmel <idosch@...lanox.com>
Subject: [RFC PATCH net-next 03/12] drop_monitor: Document scope of spinlock

From: Ido Schimmel <idosch@...lanox.com>

While 'per_cpu_dm_data' is a per-CPU variable, its 'skb' and
'send_timer' fields can be accessed concurrently by the CPU sending the
netlink notification to user space from the workqueue and the CPU
tracing kfree_skb(). This spinlock is meant to protect against that.

Document its scope and suppress the checkpatch message "spinlock_t
definition without comment".

Signed-off-by: Ido Schimmel <idosch@...lanox.com>
---
 net/core/drop_monitor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
index 000ec8b66d1e..35d31b007da4 100644
--- a/net/core/drop_monitor.c
+++ b/net/core/drop_monitor.c
@@ -52,7 +52,7 @@ static int trace_state = TRACE_OFF;
 static DEFINE_MUTEX(net_dm_mutex);
 
 struct per_cpu_dm_data {
-	spinlock_t		lock;
+	spinlock_t		lock;	/* Protects 'skb' and 'send_timer' */
 	struct sk_buff		*skb;
 	struct work_struct	dm_alert_work;
 	struct timer_list	send_timer;
-- 
2.21.0