[RFC net-next 2/2] net: net-sysfs: Reduce netstat_show read_lock critical section

[Saeed Mahameed]

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 <sae...@mellanox.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