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net: protect netdev->napi_list with netdev_lock()
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Hold netdev->lock when NAPIs are getting added or removed.
This will allow safe access to NAPI instances of a net_device
without rtnl_lock.

Create a family of helpers which assume the lock is already taken.
Switch iavf to them, as it makes extensive use of netdev->lock,
already.

Reviewed-by: Joe Damato <jdamato@fastly.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250115035319.559603-6-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
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Jakub Kicinski committed Jan 16, 2025
1 parent 5112457 commit 1b23cdb
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Showing 3 changed files with 60 additions and 15 deletions.
6 changes: 3 additions & 3 deletions drivers/net/ethernet/intel/iavf/iavf_main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -1800,8 +1800,8 @@ static int iavf_alloc_q_vectors(struct iavf_adapter *adapter)
q_vector->v_idx = q_idx;
q_vector->reg_idx = q_idx;
cpumask_copy(&q_vector->affinity_mask, cpu_possible_mask);
netif_napi_add(adapter->netdev, &q_vector->napi,
iavf_napi_poll);
netif_napi_add_locked(adapter->netdev, &q_vector->napi,
iavf_napi_poll);
}

return 0;
Expand All @@ -1827,7 +1827,7 @@ static void iavf_free_q_vectors(struct iavf_adapter *adapter)
for (q_idx = 0; q_idx < num_q_vectors; q_idx++) {
struct iavf_q_vector *q_vector = &adapter->q_vectors[q_idx];

netif_napi_del(&q_vector->napi);
netif_napi_del_locked(&q_vector->napi);
}
kfree(adapter->q_vectors);
adapter->q_vectors = NULL;
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54 changes: 47 additions & 7 deletions include/linux/netdevice.h
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Original file line number Diff line number Diff line change
Expand Up @@ -2456,7 +2456,7 @@ struct net_device {
* Drivers are free to use it for other protection.
*
* Protects:
* @net_shaper_hierarchy, @reg_state
* @napi_list, @net_shaper_hierarchy, @reg_state
*
* Partially protects (writers must hold both @lock and rtnl_lock):
* @up
Expand Down Expand Up @@ -2712,8 +2712,19 @@ static inline void netif_napi_set_irq(struct napi_struct *napi, int irq)
*/
#define NAPI_POLL_WEIGHT 64

void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int weight);
void netif_napi_add_weight_locked(struct net_device *dev,
struct napi_struct *napi,
int (*poll)(struct napi_struct *, int),
int weight);

static inline void
netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int weight)
{
netdev_lock(dev);
netif_napi_add_weight_locked(dev, napi, poll, weight);
netdev_unlock(dev);
}

/**
* netif_napi_add() - initialize a NAPI context
Expand All @@ -2731,6 +2742,13 @@ netif_napi_add(struct net_device *dev, struct napi_struct *napi,
netif_napi_add_weight(dev, napi, poll, NAPI_POLL_WEIGHT);
}

static inline void
netif_napi_add_locked(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int))
{
netif_napi_add_weight_locked(dev, napi, poll, NAPI_POLL_WEIGHT);
}

static inline void
netif_napi_add_tx_weight(struct net_device *dev,
struct napi_struct *napi,
Expand All @@ -2741,6 +2759,15 @@ netif_napi_add_tx_weight(struct net_device *dev,
netif_napi_add_weight(dev, napi, poll, weight);
}

static inline void
netif_napi_add_config_locked(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int index)
{
napi->index = index;
napi->config = &dev->napi_config[index];
netif_napi_add_weight_locked(dev, napi, poll, NAPI_POLL_WEIGHT);
}

/**
* netif_napi_add_config - initialize a NAPI context with persistent config
* @dev: network device
Expand All @@ -2752,9 +2779,9 @@ static inline void
netif_napi_add_config(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int index)
{
napi->index = index;
napi->config = &dev->napi_config[index];
netif_napi_add_weight(dev, napi, poll, NAPI_POLL_WEIGHT);
netdev_lock(dev);
netif_napi_add_config_locked(dev, napi, poll, index);
netdev_unlock(dev);
}

/**
Expand All @@ -2774,6 +2801,8 @@ static inline void netif_napi_add_tx(struct net_device *dev,
netif_napi_add_tx_weight(dev, napi, poll, NAPI_POLL_WEIGHT);
}

void __netif_napi_del_locked(struct napi_struct *napi);

/**
* __netif_napi_del - remove a NAPI context
* @napi: NAPI context
Expand All @@ -2782,7 +2811,18 @@ static inline void netif_napi_add_tx(struct net_device *dev,
* containing @napi. Drivers might want to call this helper to combine
* all the needed RCU grace periods into a single one.
*/
void __netif_napi_del(struct napi_struct *napi);
static inline void __netif_napi_del(struct napi_struct *napi)
{
netdev_lock(napi->dev);
__netif_napi_del_locked(napi);
netdev_unlock(napi->dev);
}

static inline void netif_napi_del_locked(struct napi_struct *napi)
{
__netif_napi_del_locked(napi);
synchronize_net();
}

/**
* netif_napi_del - remove a NAPI context
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15 changes: 10 additions & 5 deletions net/core/dev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -6910,9 +6910,12 @@ netif_napi_dev_list_add(struct net_device *dev, struct napi_struct *napi)
list_add_rcu(&napi->dev_list, higher); /* adds after higher */
}

void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int weight)
void netif_napi_add_weight_locked(struct net_device *dev,
struct napi_struct *napi,
int (*poll)(struct napi_struct *, int),
int weight)
{
netdev_assert_locked(dev);
if (WARN_ON(test_and_set_bit(NAPI_STATE_LISTED, &napi->state)))
return;

Expand Down Expand Up @@ -6953,7 +6956,7 @@ void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
dev->threaded = false;
netif_napi_set_irq(napi, -1);
}
EXPORT_SYMBOL(netif_napi_add_weight);
EXPORT_SYMBOL(netif_napi_add_weight_locked);

void napi_disable(struct napi_struct *n)
{
Expand Down Expand Up @@ -7024,8 +7027,10 @@ static void flush_gro_hash(struct napi_struct *napi)
}

/* Must be called in process context */
void __netif_napi_del(struct napi_struct *napi)
void __netif_napi_del_locked(struct napi_struct *napi)
{
netdev_assert_locked(napi->dev);

if (!test_and_clear_bit(NAPI_STATE_LISTED, &napi->state))
return;

Expand All @@ -7045,7 +7050,7 @@ void __netif_napi_del(struct napi_struct *napi)
napi->thread = NULL;
}
}
EXPORT_SYMBOL(__netif_napi_del);
EXPORT_SYMBOL(__netif_napi_del_locked);

static int __napi_poll(struct napi_struct *n, bool *repoll)
{
Expand Down

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