Subject: Re: [Intel-wired-lan] [PATCH net] i40e: avoid NULL pointer dereference and recursive errors on early PCI error

From: "Keller, Jacob E" <[email-masked]>
Date: Tue, 27 Sep 2016 22:41:59 +0000

On Tue, 2016-09-27 at 18:14 -0300, Guilherme G. Piccoli wrote:
> Although rare, it's possible to hit PCI error early on device
> probe, meaning possibly some structs are not entirely initialized,
> and some might even be completely uninitialized, leading to NULL
> pointer dereference.
> 
> The i40e driver currently presents a "bad" behavior if device hits
> such early PCI error: firstly, the struct i40e_pf might not be
> attached to pci_dev yet, leading to a NULL pointer dereference on
> access to pf->state.
> 

Oops! Nice find!

> Even checking if the struct is NULL and avoiding the access in that
> case isn't enough, since the driver cannot recover from PCI error
> that early; in our experiments we saw multiple failures on kernel
> log, like:
> 
>   [549.664] i40e 0007:01:00.1: Initial pf_reset failed: -15
>   [549.664] i40e: probe of 0007:01:00.1 failed with error -15
>   [...]
>   [871.644] i40e 0007:01:00.1: The driver for the device stopped
> because the
>   device firmware failed to init. Try updating your NVM image.
>   [871.644] i40e: probe of 0007:01:00.1 failed with error -32
>   [...]
>   [872.516] i40e 0007:01:00.0: ARQ: Unknown event 0x0000 ignored
> 
> Between the first probe failure (error -15) and the second (error
> -32)
> another PCI error happened due to the first bad probe. Also, driver
> started to flood console with those ARQ event messages.
> 
> This patch will prevent these issues by allowing error recovery
> mechanism to remove the failed device from the system instead of
> trying to recover from early PCI errors during device probe.
> 

This seems reasonable.

> Signed-off-by: Guilherme G. Piccoli <[email-masked]>
> ---
>  drivers/net/ethernet/intel/i40e/i40e_main.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/i40e/i40e_main.c
> b/drivers/net/ethernet/intel/i40e/i40e_main.c
> index d0b3a1b..dad15b6 100644
> --- a/drivers/net/ethernet/intel/i40e/i40e_main.c
> +++ b/drivers/net/ethernet/intel/i40e/i40e_main.c
> @@ -11360,6 +11360,12 @@ static pci_ers_result_t
> i40e_pci_error_detected(struct pci_dev *pdev,
>  
>  	dev_info(&pdev->dev, "%s: error %d\n", __func__, error);
>  
> +	if (!pf) {
> +		dev_info(&pdev->dev,
> +			 "Cannot recover - error happened during
> device probe\n");
> +		return PCI_ERS_RESULT_DISCONNECT;
> +	}
> +

Looks good to me.

Acked-by: Jacob Keller <[email-masked]>

Thanks for the bug fix and detailed explanation!

Regards,
Jake

>  	/* shutdown all operations */
>  	if (!test_bit(__I40E_SUSPENDED, &pf->state)) {
>  		rtnl_lock();