netdev - [PATCH v5 net-next 16/16] net: mark ndo_get

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Message-Id: <20210108163159.358043-17-olteanv@gmail.com>
Date:   Fri,  8 Jan 2021 18:31:59 +0200
From:   Vladimir Oltean <olteanv@...il.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>,
        Cong Wang <xiyou.wangcong@...il.com>,
        Stephen Hemminger <stephen@...workplumber.org>,
        Eric Dumazet <edumazet@...gle.com>,
        George McCollister <george.mccollister@...il.com>,
        Oleksij Rempel <o.rempel@...gutronix.de>,
        Jay Vosburgh <j.vosburgh@...il.com>,
        Veaceslav Falico <vfalico@...il.com>,
        Andy Gospodarek <andy@...yhouse.net>,
        Arnd Bergmann <arnd@...db.de>, Taehee Yoo <ap420073@...il.com>,
        Jiri Pirko <jiri@...nulli.us>, Florian Westphal <fw@...len.de>,
        Nikolay Aleksandrov <nikolay@...dia.com>,
        Pravin B Shelar <pshelar@....org>,
        Sridhar Samudrala <sridhar.samudrala@...el.com>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: [PATCH v5 net-next 16/16] net: mark ndo_get_stats64 as being able to sleep

From: Vladimir Oltean <vladimir.oltean@....com>

Now that all callers have been converted to not use atomic context when
calling dev_get_stats, it is time to update the documentation and put a
notice in the function that it expects process context.

Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
Changes in v5:
None.

Changes in v4:
None.

Changes in v3:
None.

Changes in v2:
Updated the documentation.

 Documentation/networking/netdevices.rst | 8 ++++++--
 Documentation/networking/statistics.rst | 9 ++++-----
 net/core/dev.c                          | 2 ++
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst
index 5a85fcc80c76..944599722c76 100644
--- a/Documentation/networking/netdevices.rst
+++ b/Documentation/networking/netdevices.rst
@@ -64,8 +64,12 @@ ndo_do_ioctl:
 	Context: process
 
 ndo_get_stats:
-	Synchronization: dev_base_lock rwlock.
-	Context: nominally process, but don't sleep inside an rwlock
+	Synchronization:
+		none. netif_lists_lock(net) might be held, but not guaranteed.
+		It is illegal to hold rtnl_lock() in this method, since it will
+		cause a lock inversion with netif_lists_lock and a deadlock.
+	Context:
+		process
 
 ndo_start_xmit:
 	Synchronization: __netif_tx_lock spinlock.
diff --git a/Documentation/networking/statistics.rst b/Documentation/networking/statistics.rst
index 234abedc29b2..ad3e353df0dd 100644
--- a/Documentation/networking/statistics.rst
+++ b/Documentation/networking/statistics.rst
@@ -155,11 +155,10 @@ Drivers must ensure best possible compliance with
 Please note for example that detailed error statistics must be
 added into the general `rx_error` / `tx_error` counters.
 
-The `.ndo_get_stats64` callback can not sleep because of accesses
-via `/proc/net/dev`. If driver may sleep when retrieving the statistics
-from the device it should do so periodically asynchronously and only return
-a recent copy from `.ndo_get_stats64`. Ethtool interrupt coalescing interface
-allows setting the frequency of refreshing statistics, if needed.
+Drivers may sleep when retrieving the statistics from the device, or they might
+read the counters periodically and only return in `.ndo_get_stats64` a recent
+copy collected asynchronously. In the latter case, the ethtool interrupt
+coalescing interface allows setting the frequency of refreshing statistics.
 
 Retrieving ethtool statistics is a multi-syscall process, drivers are advised
 to keep the number of statistics constant to avoid race conditions with
diff --git a/net/core/dev.c b/net/core/dev.c
index 30facac95d5e..afd0e226efd4 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10409,6 +10409,8 @@ int __must_check dev_get_stats(struct net_device *dev,
 	const struct net_device_ops *ops = dev->netdev_ops;
 	int err = 0;
 
+	might_sleep();
+
 	if (ops->ndo_get_stats64) {
 		memset(storage, 0, sizeof(*storage));
 		err = ops->ndo_get_stats64(dev, storage);
-- 
2.25.1