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Date:   Mon,  7 Dec 2020 01:59:17 +0200
From:   Vladimir Oltean <>
To:     "David S . Miller" <>,
        Jakub Kicinski <>
Cc:, Andrew Lunn <>,
        Florian Fainelli <>,
        Paul Gortmaker <>,
        Pablo Neira Ayuso <>,
        Jiri Benc <>,
        Cong Wang <>,
        Jamal Hadi Salim <>,
        Stephen Hemminger <>,
        Eric Dumazet <>,
        George McCollister <>,
        Oleksij Rempel <>,
        Christian Brauner <>
Subject: [RFC PATCH net-next 11/13] net: sysfs: don't hold dev_base_lock while 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.

I need to preface this by saying that I have no idea why netstat_show
takes the dev_base_lock rwlock. Two things can be observed:
(a) it does not appear to be due to dev_isalive requiring it for some
    reason, because broadcast_show() also calls dev_isalive() and has
    had no problem existing since the beginning of git.
(b) the dev_get_stats function definitely does not need dev_base_lock
    protection either. In fact, holding the dev_base_lock is the entire
    problem here, because we want to make dev_get_stats sleepable, and
    holding a rwlock gives us atomic context.

So since no protection seems to be necessary, just run unlocked while
retrieving the /sys/class/net/eth0/statistics/* values.

Cc: Christian Brauner <>
Cc: Eric Dumazet <>
Signed-off-by: Vladimir Oltean <>
 net/core/net-sysfs.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index 999b70c59761..0782a476b424 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -585,14 +585,13 @@ static ssize_t netstat_show(const struct device *d,
 	WARN_ON(offset > sizeof(struct rtnl_link_stats64) ||
 		offset % sizeof(u64) != 0);
-	read_lock(&dev_base_lock);
 	if (dev_isalive(dev)) {
 		struct rtnl_link_stats64 temp;
 		const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
 		ret = sprintf(buf, fmt_u64, *(u64 *)(((u8 *)stats) + offset));
-	read_unlock(&dev_base_lock);
 	return ret;

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