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net: designate queue -> napi linking as "ops protected"

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netdev netlink is the only reader of netdev_{,rx_}queue->napi,
and it already holds netdev->lock. Switch protection of
the writes to netdev->lock to "ops protected".

The expectation will be now that accessing queue->napi
will require netdev->lock for "ops locked" drivers, and
rtnl_lock for all other drivers.

Current "ops locked" drivers don't require any changes.
gve and netdevsim use _locked() helpers right next to
netif_queue_set_napi() so they must be holding the instance
lock. iavf doesn't call it. bnxt is a bit messy but all paths
seem locked.

Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Link: https://patch.msgid.link/20250324224537.248800-7-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Jakub Kicinski 2025-03-24 15:45:32 -07:00
parent 0a65dcf624
commit 310ae9eb26
4 changed files with 13 additions and 5 deletions
Download patch file Download diff file Expand all files Collapse all files

5
include/linux/netdevice.h
View file

@ -710,7 +710,7 @@ struct netdev_queue {
* slow- / control-path part
*/
/* NAPI instance for the queue
* Readers and writers must hold RTNL
* "ops protected", see comment about net_device::lock
*/
struct napi_struct *napi;
@ -2526,7 +2526,8 @@ struct net_device {
* Double ops protects:
* @real_num_rx_queues, @real_num_tx_queues
*
* Also protects some fields in struct napi_struct.
* Also protects some fields in:
* struct napi_struct, struct netdev_queue, struct netdev_rx_queue
*
* Ordering: take after rtnl_lock.
*/

8
include/net/netdev_lock.h
View file

@ -56,6 +56,14 @@ static inline void netdev_ops_assert_locked(const struct net_device *dev)
ASSERT_RTNL();
}
static inline void
netdev_ops_assert_locked_or_invisible(const struct net_device *dev)
{
if (dev->reg_state == NETREG_REGISTERED ||
dev->reg_state == NETREG_UNREGISTERING)
netdev_ops_assert_locked(dev);
}
static inline int netdev_lock_cmp_fn(const struct lockdep_map *a,
const struct lockdep_map *b)
{

2
include/net/netdev_rx_queue.h
View file

@ -24,7 +24,7 @@ struct netdev_rx_queue {
struct xsk_buff_pool *pool;
#endif
/* NAPI instance for the queue
* Readers and writers must hold RTNL
* "ops protected", see comment about net_device::lock
*/
struct napi_struct *napi;
struct pp_memory_provider_params mp_params;

3
net/core/dev.c
View file

@ -6901,8 +6901,7 @@ void netif_queue_set_napi(struct net_device *dev, unsigned int queue_index,
if (WARN_ON_ONCE(napi && !napi->dev))
return;
if (dev->reg_state >= NETREG_REGISTERED)
ASSERT_RTNL();
netdev_ops_assert_locked_or_invisible(dev);
switch (type) {
case NETDEV_QUEUE_TYPE_RX: