netdev - Re: [PATCH 1/1] net/mlx5: Call pci_disable

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Date:   Thu, 30 Apr 2020 21:47:48 +0200
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Saeed Mahameed <saeedm@...lanox.com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "leon@...nel.org" <leon@...nel.org>
Subject: Re: [PATCH 1/1] net/mlx5: Call pci_disable_sriov() on remove



On 4/30/20 5:58 PM, Saeed Mahameed wrote:
> On Thu, 2020-04-30 at 14:03 +0200, Niklas Schnelle wrote:
>> as described in Documentation/PCI/pci-iov-howto.rst a driver with SR-
>> IOV
>> support should call pci_disable_sriov() in the remove handler.
> 
> Hi Niklas,
> 
> looking at the documentation, it doesn't say "should" it just gives the
> code as example.
> 
>> Otherwise removing a PF (e.g. via pci_stop_and_remove_bus_device())
>> with
>> attached VFs does not properly shut the VFs down before shutting down
>> the PF. This leads to the VF drivers handling defunct devices and
>> accompanying error messages.
>>
> 
> Which should be the admin responsibility .. if the admin want to do
> this, then let it be.. why block him ? 
> 
> our mlx5 driver in the vf handles this gracefully and once pf
> driver/device is back online the vf driver quickly recovers.
See my answer to your other answer ;-)
> 
>> In the current code pci_disable_sriov() is already called in
>> mlx5_sriov_disable() but not in mlx5_sriov_detach() which is called
>> from
>> the remove handler. Fix this by moving the pci_disable_sriov() call
>> into
>> mlx5_device_disable_sriov() which is called by both.
>>
>> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
>> ---
>>  drivers/net/ethernet/mellanox/mlx5/core/sriov.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/sriov.c
>> b/drivers/net/ethernet/mellanox/mlx5/core/sriov.c
>> index 3094d20297a9..2401961c9f5b 100644
>> --- a/drivers/net/ethernet/mellanox/mlx5/core/sriov.c
>> +++ b/drivers/net/ethernet/mellanox/mlx5/core/sriov.c
>> @@ -114,6 +114,8 @@ mlx5_device_disable_sriov(struct mlx5_core_dev
>> *dev, int num_vfs, bool clear_vf)
>>  	int err;
>>  	int vf;
>>  
>> +	pci_disable_sriov(dev->pdev);
>> +
>>  	for (vf = num_vfs - 1; vf >= 0; vf--) {
>>  		if (!sriov->vfs_ctx[vf].enabled)
>>  			continue;
>> @@ -156,7 +158,6 @@ static void mlx5_sriov_disable(struct pci_dev
>> *pdev)
>>  	struct mlx5_core_dev *dev  = pci_get_drvdata(pdev);
>>  	int num_vfs = pci_num_vf(dev->pdev);
>>  
>> -	pci_disable_sriov(pdev);
> 
> this patch is no good as it breaks code symmetry.. and could lead to
> many new issues.
Ah you're right I totally missed that there is a matching pci_enable_sriov() in
mlx5_enable_sriov() haven't used these myself before and since it wasn't in the
documentation example I somehow expected it to happen in non-driver code,
so for symmetry that would also have to move to mlx5_device_enable_sriov(),
sorry for the oversight.
> 
> 
>>  	mlx5_device_disable_sriov(dev, num_vfs, true);
>>  }
>>  
>