linux-kernel - Re: [PATCH V2 net 06/20] net/ena: fix NULL dereference when removing the driver after device reset faild

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Date:   Mon, 5 Dec 2016 20:30:44 +0200
From:   Netanel Belgazal <netanel@...apurnalabs.com>
To:     Matt Wilson <msw@...n.com>
Cc:     linux-kernel@...r.kernel.org, davem@...emloft.net,
        netdev@...r.kernel.org, dwmw@...zon.com, zorik@...apurnalabs.com,
        alex@...apurnalabs.com, saeed@...apurnalabs.com, msw@...zon.com,
        aliguori@...zon.com, nafea@...apurnalabs.com
Subject: Re: [PATCH V2 net 06/20] net/ena: fix NULL dereference when removing
 the driver after device reset faild



On 12/05/2016 06:29 AM, Matt Wilson wrote:
> On Sun, Dec 04, 2016 at 03:19:24PM +0200, Netanel Belgazal wrote:
>> If for some reason the device stop responding and the device reset failed
>> to recover the device, the mmio register read datastructure will not be
>> reinitialized.
> If for some reason the device stops responding, and the device reset
> fails to recover the device, the MMIO register read data structure
> will not be reinitialized.

OK
>
>> On driver removal, the driver will also tries to reset the device
>> but this time the mmio data structure will be NULL.
> On driver removal, the driver will also try to reset the device, but
> this time the MMIO data structure will be NULL.
OK
>> To solve this issue perform the device reset in the remove function only if
>> the device is runnig.
> To solve this issue, perform the device reset in the remove function
> only if the device is running.
>
> Do you have an example of the NULL pointer dereference that you can
> paste in? It can be helpful for those searching for a fix for a bug
> they've experienced.
I'll add a crash dump.

> --msw
>
>> Signed-off-by: Netanel Belgazal <netanel@...apurnalabs.com>
>> ---
>>   drivers/net/ethernet/amazon/ena/ena_netdev.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> index 224302c..ad5f78f 100644
>> --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
>> @@ -2516,6 +2516,8 @@ static void ena_fw_reset_device(struct work_struct *work)
>>   err:
>>   	rtnl_unlock();
>>   
>> +	clear_bit(ENA_FLAG_DEVICE_RUNNING, &adapter->flags);
>> +
>>   	dev_err(&pdev->dev,
>>   		"Reset attempt failed. Can not reset the device\n");
>>   }
>> @@ -3126,7 +3128,9 @@ static void ena_remove(struct pci_dev *pdev)
>>   
>>   	cancel_work_sync(&adapter->resume_io_task);
>>   
>> -	ena_com_dev_reset(ena_dev);
>> +	/* Reset the device only if the device is running. */
>> +	if (test_bit(ENA_FLAG_DEVICE_RUNNING, &adapter->flags))
>> +		ena_com_dev_reset(ena_dev);
>>   
>>   	ena_free_mgmnt_irq(adapter);
>>