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Date:   Mon,  7 Dec 2020 01:59:16 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, Andrew Lunn <andrew@...n.ch>,
        Florian Fainelli <f.fainelli@...il.com>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Jiri Benc <jbenc@...hat.com>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <edumazet@...gle.com>,
        George McCollister <george.mccollister@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>
Subject: [RFC PATCH net-next 10/13] net: procfs: hold the netdev lists lock when retrieving device statistics

In the effort of making .ndo_get_stats64 be able to sleep, we need to
ensure the callers of dev_get_stats do not use atomic context.

The /proc/net/dev file uses an RCU read-side critical section to ensure
the integrity of the list of network interfaces, because it iterates
through all net devices in the netns to show their statistics.

To offer the equivalent protection against an interface registering or
deregistering, while also remaining in sleepable context, we can use the
netns mutex for the interface lists.

Cc: Cong Wang <xiyou.wangcong@...il.com>
Cc: Eric Dumazet <edumazet@...gle.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 net/core/net-procfs.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/core/net-procfs.c b/net/core/net-procfs.c
index c714e6a9dad4..83f8a89dfc5a 100644
--- a/net/core/net-procfs.c
+++ b/net/core/net-procfs.c
@@ -21,7 +21,7 @@ static inline struct net_device *dev_from_same_bucket(struct seq_file *seq, loff
 	unsigned int count = 0, offset = get_offset(*pos);
 
 	h = &net->dev_index_head[get_bucket(*pos)];
-	hlist_for_each_entry_rcu(dev, h, index_hlist) {
+	hlist_for_each_entry(dev, h, index_hlist) {
 		if (++count == offset)
 			return dev;
 	}
@@ -51,9 +51,11 @@ static inline struct net_device *dev_from_bucket(struct seq_file *seq, loff_t *p
  *	in detail.
  */
 static void *dev_seq_start(struct seq_file *seq, loff_t *pos)
-	__acquires(RCU)
 {
-	rcu_read_lock();
+	struct net *net = seq_file_net(seq);
+
+	mutex_lock(&net->netdev_lists_lock);
+
 	if (!*pos)
 		return SEQ_START_TOKEN;
 
@@ -70,9 +72,10 @@ static void *dev_seq_next(struct seq_file *seq, void *v, loff_t *pos)
 }
 
 static void dev_seq_stop(struct seq_file *seq, void *v)
-	__releases(RCU)
 {
-	rcu_read_unlock();
+	struct net *net = seq_file_net(seq);
+
+	mutex_unlock(&net->netdev_lists_lock);
 }
 
 static void dev_seq_printf_stats(struct seq_file *seq, struct net_device *dev)
-- 
2.25.1

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