答复: [外部邮件] [PATCH net-next V3] net/mlx5: Expedite notifier unregistration during device teardown

[Li,Rongqing]

> 
> From: Li RongQing <lirongqing@xxxxxxxxx>
> 
> During device hot-unplug, the mlx5 driver expects quickly unregister
> notification chains. The standard atomic_notifier_chain_unregister()
> calls synchronize_rcu(), which introduces significant latency and can become
> a bottleneck during mass resource cleanup.
> 
> Introduce atomic_notifier_chain_unregister_expedited() to leverage
> synchronize_rcu_expedited(), and use it significantly reducing wait times in
> the following paths:
>  - Event Queue (EQ) notifier chain
>  - Firmware event notifier chain
>  - IRQ notifier chain
> 
> On x86-64 with HZ=1000, 64 networking channels:
> - Average teardown time: 3.59s -> 1.9s (47% reduction) On x86-64 with
> HZ=250, 64 networking channels:
> - Average teardown time: 5.5s -> 1.9s (65% reduction)
> 
> Co-developed-by: liyongkang <liyongkang01@xxxxxxxxx>
> Signed-off-by: liyongkang <liyongkang01@xxxxxxxxx>
> Signed-off-by: Li RongQing <lirongqing@xxxxxxxxx>
> Signed-off-by: Tariq Toukan <tariqt@xxxxxxxxxx>
> ---
> V3: rebased.
> 
> V2:
> https://lore.kernel.org/all/20260317003544.2583-1-lirongqing@xxxxxxxxx/
> 
> drivers/net/ethernet/mellanox/mlx5/core/eq.c  |  2
> +-  .../net/ethernet/mellanox/mlx5/core/events.c  |  2
> +-  .../net/ethernet/mellanox/mlx5/core/pci_irq.c |  2 +-
>  include/linux/notifier.h                      |  2 ++
>  kernel/notifier.c                             | 24
> +++++++++++++++++++
>  5 files changed, 29 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> index d11ec263d53c..c86090cb58c6 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/eq.c
> @@ -1243,6 +1243,6 @@ int mlx5_eq_notifier_unregister(struct
> mlx5_core_dev *dev, struct mlx5_nb *nb)  {
>  	struct mlx5_eq_table *eqt = dev->priv.eq_table;
> 
> -	return atomic_notifier_chain_unregister(&eqt->nh[nb->event_type],
> &nb->nb);
> +	return
> +atomic_notifier_chain_unregister_expedited(&eqt->nh[nb->event_type],
> +&nb->nb);
>  }
>  EXPORT_SYMBOL(mlx5_eq_notifier_unregister);
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/events.c
> b/drivers/net/ethernet/mellanox/mlx5/core/events.c
> index 4d7f35b96876..753cb15cdeee 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/events.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/events.c
> @@ -436,7 +436,7 @@ int mlx5_notifier_unregister(struct mlx5_core_dev
> *dev, struct notifier_block *n  {
>  	struct mlx5_events *events = dev->priv.events;
> 
> -	return atomic_notifier_chain_unregister(&events->fw_nh, nb);
> +	return atomic_notifier_chain_unregister_expedited(&events->fw_nh,
> nb);
>  }
>  EXPORT_SYMBOL(mlx5_notifier_unregister);
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c
> b/drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c
> index 0f5b8bc7861e..cb31e8c7a244 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/pci_irq.c
> @@ -343,7 +343,7 @@ int mlx5_irq_detach_nb(struct mlx5_irq *irq, struct
> notifier_block *nb)  {
>  	int err = 0;
> 
> -	err = atomic_notifier_chain_unregister(&irq->nh, nb);
> +	err = atomic_notifier_chain_unregister_expedited(&irq->nh, nb);
>  	mlx5_irq_put(irq);
>  	return err;
>  }
> diff --git a/include/linux/notifier.h b/include/linux/notifier.h index
> 01b6c9d9956f..156d958f98f0 100644
> --- a/include/linux/notifier.h
> +++ b/include/linux/notifier.h
> @@ -159,6 +159,8 @@ extern int
> blocking_notifier_chain_register_unique_prio(
> 
>  extern int atomic_notifier_chain_unregister(struct atomic_notifier_head
> *nh,
>  		struct notifier_block *nb);
> +extern int atomic_notifier_chain_unregister_expedited(struct
> atomic_notifier_head *nh,
> +		struct notifier_block *nb);
>  extern int blocking_notifier_chain_unregister(struct blocking_notifier_head
> *nh,
>  		struct notifier_block *nb);
>  extern int raw_notifier_chain_unregister(struct raw_notifier_head *nh, diff
> --git a/kernel/notifier.c b/kernel/notifier.c index 2f9fe7c30287..9b35822fc2c0
> 100644
> --- a/kernel/notifier.c
> +++ b/kernel/notifier.c
> @@ -197,6 +197,30 @@ int atomic_notifier_chain_unregister(struct
> atomic_notifier_head *nh,  }
> EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister);
> 
> +/**
> + *	atomic_notifier_chain_unregister_expedited - Remove notifier from an
> atomic notifier chain
> + *	@nh: Pointer to head of the atomic notifier chain
> + *	@n: Entry to remove from notifier chain
> + *
> + *	Removes a notifier from an atomic notifier chain and forcefully
> + *	accelerates the RCU grace period.
> + *
> + *	Return: 0 on success, or -ENOENT on failure.
> + */
> +int atomic_notifier_chain_unregister_expedited(struct atomic_notifier_head
> *nh,
> +		struct notifier_block *n)
> +{
> +	unsigned long flags;
> +	int ret;
> +
> +	spin_lock_irqsave(&nh->lock, flags);
> +	ret = notifier_chain_unregister(&nh->head, n);
> +	spin_unlock_irqrestore(&nh->lock, flags);
> +	synchronize_rcu_expedited();
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(atomic_notifier_chain_unregister_expedited);
> +
>  /**
>   *	atomic_notifier_call_chain - Call functions in an atomic notifier chain
>   *	@nh: Pointer to head of the atomic notifier chain
> 
> base-commit: d67e5dbda22604d0fcde32fce58c65f88676e676
> --
> 2.44.0

The netdev/build_allmodconfig_warn bot reports a new sparse warning at line 217:

../kernel/notifier.c:217:42: warning: incorrect type in argument 1 (different address spaces)

This is not a new class of problem. The same warning already exists throughout notifier.c on every notifier-chain helper call site:

    ../kernel/notifier.c:148:40: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:171:40: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:193:42: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:217:42: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:247:36: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:285:49: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:288:40: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:348:51: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:351:42: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:369:51: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:404:44: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:429:41: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:446:43: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:453:44: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:477:37: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:507:49: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:510:40: warning: incorrect type in argument 1 (different address spaces)
    ../kernel/notifier.c:537:51: warning: incorrect type in argument 1 (different address spaces)

The new function added by this change simply follows the existing pattern, so it adds one more instance of an already-present warning rather than introducing a new issue.

Root cause: the notifier_chain_*() helpers take a plain struct notifier_block **, whereas the chain heads (nh->head) and the notifier_block::next links are annotated __rcu. Passing &nh->head drops the __rcu annotation at the helper boundary, and that annotation mismatch is all sparse is flagging.

This is safe. The helpers walk the list under the chain's write-side lock and publish updates via rcu_assign_pointer(), while the read/traversal path uses rcu_dereference_raw(). RCU correctness is therefore fully preserved; only the compile-time annotation is lost across the pointer-to-pointer argument. __rcu is a sparse-only attribute with no codegen effect, so the generated code is identical either way.

Cleaning this up properly would mean annotating the nl parameter of the notifier_chain_*() helpers as __rcu and using rcu_dereference_raw() for the bare reads, which touches all chain types (atomic/blocking/raw/srcu) and is orthogonal to this change.

thanks

[Li,Rongqing]