netdev - [RFC net-next 2/2] net: net-sysfs: Reduce netstat_show read

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Date:   Tue, 10 Apr 2018 10:08:12 -0700
From:   Saeed Mahameed <saeedm@...lanox.com>
To:     netdev@...r.kernel.org
Cc:     Saeed Mahameed <saeedm@...lanox.com>
Subject: [RFC net-next 2/2] net: net-sysfs: Reduce netstat_show read_lock critical section

Instead of holding the device chain read_lock also while calling
dev_get_stats just hold it only to check dev_isalive, if the dev is alive,
hold that dev via dev_hold then release the read_lock.

When done handling the device, dev_put it.

Signed-off-by: Saeed Mahameed <saeedm@...lanox.com>
---
 net/core/net-sysfs.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
index c476f0794132..ee6f9fed43df 100644
--- a/net/core/net-sysfs.c
+++ b/net/core/net-sysfs.c
@@ -563,13 +563,20 @@ static ssize_t netstat_show(const struct device *d,
 		offset % sizeof(u64) != 0);
 
 	read_lock(&dev_base_lock);
-	if (dev_isalive(dev)) {
+	if (dev_isalive(dev))
+		dev_hold(dev);
+	else
+		dev = NULL;
+	read_unlock(&dev_base_lock);
+
+	if (dev) {
 		struct rtnl_link_stats64 temp;
 		const struct rtnl_link_stats64 *stats = dev_get_stats(dev, &temp);
 
+		dev_put(dev);
 		ret = sprintf(buf, fmt_u64, *(u64 *)(((u8 *)stats) + offset));
 	}
-	read_unlock(&dev_base_lock);
+
 	return ret;
 }
 
-- 
2.14.3