netdev - Re: [PATCH net-next 03/10] mlx4: Replace the mlx4_interface.event callback with a notifier

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Date: Tue, 8 Aug 2023 14:13:02 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: Zhu Yanjun <yanjun.zhu@...ux.dev>
Cc: tariqt@...dia.com, yishaih@...dia.com, leon@...nel.org,
 davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
 pabeni@...hat.com, jgg@...pe.ca, netdev@...r.kernel.org,
 linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 03/10] mlx4: Replace the mlx4_interface.event
 callback with a notifier

On 8/5/23 16:29, Zhu Yanjun wrote:
> 在 2023/8/4 23:05, Petr Pavlu 写道:
>> Use a notifier to implement mlx4_dispatch_event() in preparation to
>> switch mlx4_en and mlx4_ib to be an auxiliary device.
>>
>> A problem is that if the mlx4_interface.event callback was replaced with
>> something as mlx4_adrv.event then the implementation of
>> mlx4_dispatch_event() would need to acquire a lock on a given device
>> before executing this callback. That is necessary because otherwise
>> there is no guarantee that the associated driver cannot get unbound when
>> the callback is running. However, taking this lock is not possible
>> because mlx4_dispatch_event() can be invoked from the hardirq context.
>> Using an atomic notifier allows the driver to accurately record when it
>> wants to receive these events and solves this problem.
>>
>> A handler registration is done by both mlx4_en and mlx4_ib at the end of
>> their mlx4_interface.add callback. This matches the current situation
>> when mlx4_add_device() would enable events for a given device
>> immediately after this callback, by adding the device on the
>> mlx4_priv.list.
>>
>> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
>> Tested-by: Leon Romanovsky <leon@...nel.org>
>> ---
>>   drivers/infiniband/hw/mlx4/main.c            | 41 +++++++++++++-------
>>   drivers/infiniband/hw/mlx4/mlx4_ib.h         |  2 +
>>   drivers/net/ethernet/mellanox/mlx4/en_main.c | 25 ++++++++----
>>   drivers/net/ethernet/mellanox/mlx4/intf.c    | 24 ++++++++----
>>   drivers/net/ethernet/mellanox/mlx4/main.c    |  2 +
>>   drivers/net/ethernet/mellanox/mlx4/mlx4.h    |  2 +
>>   drivers/net/ethernet/mellanox/mlx4/mlx4_en.h |  2 +
>>   include/linux/mlx4/driver.h                  |  8 +++-
>>   8 files changed, 76 insertions(+), 30 deletions(-)
>>
>> diff --git a/drivers/infiniband/hw/mlx4/main.c b/drivers/infiniband/hw/mlx4/main.c
>> index 7dd70d778b6b..458b4b11dffa 100644
>> --- a/drivers/infiniband/hw/mlx4/main.c
>> +++ b/drivers/infiniband/hw/mlx4/main.c
>> @@ -82,6 +82,8 @@ static const char mlx4_ib_version[] =
>>   static void do_slave_init(struct mlx4_ib_dev *ibdev, int slave, int do_init);
>>   static enum rdma_link_layer mlx4_ib_port_link_layer(struct ib_device *device,
>>   						    u32 port_num);
>> +static int mlx4_ib_event(struct notifier_block *this, unsigned long event,
>> +			 void *ptr);
>>   
>>   static struct workqueue_struct *wq;
>>   
>> @@ -2836,6 +2838,12 @@ static void *mlx4_ib_add(struct mlx4_dev *dev)
>>   				do_slave_init(ibdev, j, 1);
>>   		}
>>   	}
>> +
>> +	/* register mlx4 core notifier */
>> +	ibdev->mlx_nb.notifier_call = mlx4_ib_event;
>> +	err = mlx4_register_event_notifier(dev, &ibdev->mlx_nb);
>> +	WARN(err, "failed to register mlx4 event notifier (%d)", err);
>> +
>>   	return ibdev;
>>   
>>   err_notif:
>> @@ -2953,6 +2961,8 @@ static void mlx4_ib_remove(struct mlx4_dev *dev, void *ibdev_ptr)
>>   	int p;
>>   	int i;
>>   
>> +	mlx4_unregister_event_notifier(dev, &ibdev->mlx_nb);
>> +
>>   	mlx4_foreach_port(i, dev, MLX4_PORT_TYPE_IB)
>>   		devlink_port_type_clear(mlx4_get_devlink_port(dev, i));
>>   	ibdev->ib_active = false;
>> @@ -3173,11 +3183,14 @@ void mlx4_sched_ib_sl2vl_update_work(struct mlx4_ib_dev *ibdev,
>>   	}
>>   }
>>   
>> -static void mlx4_ib_event(struct mlx4_dev *dev, void *ibdev_ptr,
>> -			  enum mlx4_dev_event event, unsigned long param)
>> +static int mlx4_ib_event(struct notifier_block *this,
>> +			 unsigned long event /*mlx4_dev_event*/, void *ptr)
> 
> /*mlx4_dev_event*/ should be removed?

The comment was meant to indicate the actual type of the event. I can
remove it.

Thanks,
Petr