Re: [PATCH v1] net/mlx4: fix 'show port info all' during detach

[Adrien Mazarguil <adrien.mazarguil@6wind.com>]

On Wed, Feb 28, 2018 at 04:47:30PM +0000, Ophir Munk wrote:
> The following scenario causes a crash in function mlx4_get_ifname
> 1. On testpmd startup mlx4 device is probed and started
> 2. mlx4 sriov is disabled. As a result an RMV event is sent to
> testpmd which closes the device and nullify the priv struct
> members.
> 3. Running 'show port info all' in testpmd results in segmentation
> fault because of accessing NULL pointer priv->ctx
> 
> The fix is to return with an error from mlx4_get_ifname() if priv->ctx
> member is NULL.

So priv->ctx is NULL after mlx4_dev_close() was called. In my opinion the
fact testpmd is allowed to call rte_eth_dev_info_get() on a closed port is
fishy, there are quite a few other ethdev callbacks that may end up
crashing in such a scenario.

Since commit 284c908cc588 ("app/testpmd: request device removal interrupt"),
testpmd automatically calls rte_eth_dev_close() and rte_eal_dev_detach()
after receiving a removal event on a port.

rte_eth_dev_close() documentation says:

 "Close a stopped Ethernet device. The device cannot be restarted!
  The function frees all resources except for needed by the
  closed state. To free these resources, call rte_eth_dev_detach()."

Unfortunately testpmd calls rte_*eal*_dev_detach() not
rte_*eth*_dev_detach(), the former doesn't release ethdev ports while the
latter does. I think it's a mistake, there's no point in keeping a closed
device around after it's been physically unplugged.

In short, rmv_event_callback() should call detach_port() instead of
rte_eal_dev_detach().

> Fixes: 61cbdd419478 ("net/mlx4: separate device control functions")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Ophir Munk <ophirmu@mellanox.com>

The above suggests the problem is actually in testpmd and was introduced in
v17.05 by commit 284c908cc588. The proposed patch is a workaround that
doesn't address the underlying issue, thus NACK unless proven otherwise :)

> ---
>  drivers/net/mlx4/mlx4_ethdev.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/net/mlx4/mlx4_ethdev.c b/drivers/net/mlx4/mlx4_ethdev.c
> index 3bc6927..cca5223 100644
> --- a/drivers/net/mlx4/mlx4_ethdev.c
> +++ b/drivers/net/mlx4/mlx4_ethdev.c
> @@ -67,6 +67,9 @@ mlx4_get_ifname(const struct priv *priv, char (*ifname)[IF_NAMESIZE])
>  	char match[IF_NAMESIZE] = "";
>  
>  	{
> +		if (priv->ctx == NULL)
> +			return -ENOENT;
> +
>  		MKSTR(path, "%s/device/net", priv->ctx->device->ibdev_path);
>  
>  		dir = opendir(path);
> -- 
> 2.7.4
> 

-- 
Adrien Mazarguil
6WIND