netdev - Re: [PATCH net-next 6/9] ibmvnic: Use bitmap for LTB map

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Date:   Tue, 31 Aug 2021 18:33:52 -0700
From:   Dany Madden <drt@...ux.ibm.com>
To:     Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Cc:     netdev@...r.kernel.org, Brian King <brking@...ux.ibm.com>,
        cforno12@...ux.ibm.com, Rick Lindsley <ricklind@...ux.ibm.com>
Subject: Re: [PATCH net-next 6/9] ibmvnic: Use bitmap for LTB map_ids

On 2021-08-31 17:08, Sukadev Bhattiprolu wrote:
> In a follow-on patch, we will reuse long term buffers when possible.
> When doing so we have to be careful to properly assign map ids. We
> can no longer assign them sequentially because a lower map id may be
> available and we could wrap at 255 and collide with an in-use map id.
> 
> Instead, use a bitmap to track active map ids and to find a free map 
> id.
> Don't need to take locks here since the map_id only changes during 
> reset
> and at that time only the reset worker thread should be using the 
> adapter.
> 
> Noticed this when analyzing an error Dany Madden ran into with the
> patch set.
> 
> Reported-by: Dany Madden <drt@...ux.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Reviewed-by: Dany Madden <drt@...ux.ibm.com>

> ---
>  drivers/net/ethernet/ibm/ibmvnic.c | 12 ++++++++----
>  drivers/net/ethernet/ibm/ibmvnic.h |  3 ++-
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
> b/drivers/net/ethernet/ibm/ibmvnic.c
> index 8894afdb3cb3..30153a8bb5ec 100644
> --- a/drivers/net/ethernet/ibm/ibmvnic.c
> +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> @@ -228,8 +228,9 @@ static int alloc_long_term_buff(struct
> ibmvnic_adapter *adapter,
>  		dev_err(dev, "Couldn't alloc long term buffer\n");
>  		return -ENOMEM;
>  	}
> -	ltb->map_id = adapter->map_id;
> -	adapter->map_id++;
> +	ltb->map_id = find_first_zero_bit(adapter->map_ids,
> +					  MAX_MAP_ID);
> +	bitmap_set(adapter->map_ids, ltb->map_id, 1);
> 
>  	mutex_lock(&adapter->fw_lock);
>  	adapter->fw_done_rc = 0;
> @@ -284,6 +285,8 @@ static void free_long_term_buff(struct
> ibmvnic_adapter *adapter,
>  	dma_free_coherent(dev, ltb->size, ltb->buff, ltb->addr);
> 
>  	ltb->buff = NULL;
> +	/* mark this map_id free */
> +	bitmap_clear(adapter->map_ids, ltb->map_id, 1);
>  	ltb->map_id = 0;
>  }
> 
> @@ -1231,8 +1234,6 @@ static int init_resources(struct ibmvnic_adapter 
> *adapter)
>  		return rc;
>  	}
> 
> -	adapter->map_id = 1;
> -
>  	rc = init_napi(adapter);
>  	if (rc)
>  		return rc;
> @@ -5553,6 +5554,9 @@ static int ibmvnic_probe(struct vio_dev *dev,
> const struct vio_device_id *id)
>  	adapter->vdev = dev;
>  	adapter->netdev = netdev;
>  	adapter->login_pending = false;
> +	memset(&adapter->map_ids, 0, sizeof(adapter->map_ids));
> +	/* map_ids start at 1, so ensure map_id 0 is always "in-use" */
> +	bitmap_set(adapter->map_ids, 0, 1);
> 
>  	ether_addr_copy(adapter->mac_addr, mac_addr_p);
>  	ether_addr_copy(netdev->dev_addr, adapter->mac_addr);
> diff --git a/drivers/net/ethernet/ibm/ibmvnic.h
> b/drivers/net/ethernet/ibm/ibmvnic.h
> index 5652566818fb..e97f1aa98c05 100644
> --- a/drivers/net/ethernet/ibm/ibmvnic.h
> +++ b/drivers/net/ethernet/ibm/ibmvnic.h
> @@ -979,7 +979,8 @@ struct ibmvnic_adapter {
>  	u64 opt_tx_entries_per_subcrq;
>  	u64 opt_rxba_entries_per_subcrq;
>  	__be64 tx_rx_desc_req;
> -	u8 map_id;
> +#define MAX_MAP_ID	255
> +	DECLARE_BITMAP(map_ids, MAX_MAP_ID);
>  	u32 num_active_rx_scrqs;
>  	u32 num_active_rx_pools;
>  	u32 num_active_rx_napi;