[RFC PATCH net-next 12/13] net: mark ndo_get_stats64 as being able to sleep

Vladimir Oltean
2020-12-07T00:02:19Z

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@nxp.com>
---
Documentation/networking/netdevices.rst | 4 ++--
Documentation/networking/statistics.rst | 9 ++++-----
net/core/dev.c | 2 ++
3 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/Documentation/networking/netdevices.rst b/Documentation/networking/netdevices.rst
index 5a85fcc80c76..9d005cbf84f7 100644
--- a/Documentation/networking/netdevices.rst
+++ b/Documentation/networking/netdevices.rst
@@ -64,8 +64,8 @@ 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. rtnl_lock() might be held, but not guaranteed.
+ 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 18904acb7797..45a845526b64 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -10367,6 +10367,8 @@ struct rtnl_link_stats64 *dev_get_stats(struct net_device *dev,
{
const struct net_device_ops *ops = dev->netdev_ops;

+ might_sleep();
+
if (ops->ndo_get_stats64) {
memset(storage, 0, sizeof(*storage));
ops->ndo_get_stats64(dev, storage);
--
2.25.1