linux-kernel - Re: [PATCH] qlcnic: check pci_reset

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Date:   Thu, 6 Apr 2023 18:06:49 +0300
From:   Denis Plotnikov <den-plotnikov@...dex-team.ru>
To:     Simon Horman <simon.horman@...igine.com>
Cc:     Bjorn Helgaas <helgaas@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, shshaikh@...vell.com,
        manishc@...vell.com, GR-Linux-NIC-Dev@...vell.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, Bjorn Helgaas <bhelgaas@...gle.com>,
        linux-pci@...r.kernel.org
Subject: Re: [PATCH] qlcnic: check pci_reset_function result


On 06.04.2023 14:43, Simon Horman wrote:
> On Thu, Apr 06, 2023 at 12:23:49PM +0300, Denis Plotnikov wrote:
>> On 06.04.2023 10:03, Simon Horman wrote:
>>> On Wed, Apr 05, 2023 at 02:37:08PM -0500, Bjorn Helgaas wrote:
>>>> On Wed, Apr 05, 2023 at 03:04:39PM +0200, Simon Horman wrote:
>>>>> On Mon, Apr 03, 2023 at 01:58:49PM +0300, Denis Plotnikov wrote:
>>>>>> On 31.03.2023 20:52, Simon Horman wrote:
>>>>>>> On Fri, Mar 31, 2023 at 11:06:05AM +0300, Denis Plotnikov wrote:
>>>>>>>> Static code analyzer complains to unchecked return value.
>>>>>>>> It seems that pci_reset_function return something meaningful
>>>>>>>> only if "reset_methods" is set.
>>>>>>>> Even if reset_methods isn't used check the return value to avoid
>>>>>>>> possible bugs leading to undefined behavior in the future.
>>>>>>>>
>>>>>>>> Signed-off-by: Denis Plotnikov <den-plotnikov@...dex-team.ru>
>>>>>>> nit: The tree this patch is targeted at should be designated, probably
>>>>>>>         net-next, so the '[PATCH net-next]' in the subject.
>>>>>>>
>>>>>>>> ---
>>>>>>>>     drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c | 4 +++-
>>>>>>>>     1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>>
>>>>>>>> diff --git a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
>>>>>>>> index 87f76bac2e463..39ecfc1a1dbd0 100644
>>>>>>>> --- a/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
>>>>>>>> +++ b/drivers/net/ethernet/qlogic/qlcnic/qlcnic_ctx.c
>>>>>>>> @@ -628,7 +628,9 @@ int qlcnic_fw_create_ctx(struct qlcnic_adapter *dev)
>>>>>>>>     	int i, err, ring;
>>>>>>>>     	if (dev->flags & QLCNIC_NEED_FLR) {
>>>>>>>> -		pci_reset_function(dev->pdev);
>>>>>>>> +		err = pci_reset_function(dev->pdev);
>>>>>>>> +		if (err && err != -ENOTTY)
>>>>>>> Are you sure about the -ENOTTY part?
>>>>>>>
>>>>>>> It seems odd to me that an FLR would be required but reset is not supported.
>>>>>> No, I'm not sure. My logic is: if the reset method isn't set than
>>>>>> pci_reset_function() returns -ENOTTY so treat that result as ok.
>>>>>> pci_reset_function may return something different than -ENOTTY only if
>>>>>> pci_reset_fn_methods[m].reset_fn is set.
>>>>> I see your reasoning: -ENOTTY means nothing happened, and probably that is ok.
>>>>> I think my main question is if that can ever happen.
>>>>> If that is unknown, then I think this conservative approach makes sense.
>>>> The commit log mentions "reset_methods", which I don't think is really
>>>> relevant here because reset_methods is an internal implementation
>>>> detail.  The point is that pci_reset_function() returns 0 if it was
>>>> successful and a negative value if it failed.
>>>>
>>>> If the driver thinks the device needs to be reset, ignoring any
>>>> negative return value seems like a mistake because the device was not
>>>> reset.
>>>>
>>>> If the reset is required for a firmware update to take effect, maybe a
>>>> diagnostic would be helpful if it fails, e.g., the other "Adapter
>>>> initialization failed.  Please reboot" messages.
>>>>
>>>> "QLCNIC_NEED_FLR" suggests that the driver expects an FLR (as opposed
>>>> to other kinds of reset).  If the driver knows that all qlcnic devices
>>>> support FLR, it could use pcie_flr() directly.
>>>>
>>>> pci_reset_function() does have the possibility that the reset works on
>>>> some devices but not all.  Secondary Bus Reset fails if there are
>>>> other functions on the same bus, e.g., a multi-function device.  And
>>>> there's some value in doing the reset the same way in all cases.
>>>>
>>>> So I would suggest something like:
>>>>
>>>>     if (dev->flags & QLCNIC_NEED_FLR) {
>>>>       err = pcie_flr(dev->pdev);
>>>>       if (err) {
>>>>         dev_err(&pdev->dev, "Adapter reset failed (%d). Please reboot\n", err);
>>>>         return err;
>>>>       }
>>>>       dev->flags &= ~QLCNIC_NEED_FLR;
>>>>     }
>>>>
>>>> Or, if there are qlcnic devices that don't support FLR:
>>>>
>>>>     if (dev->flags & QLCNIC_NEED_FLR) {
>>>>       err = pci_reset_function(dev->pdev);
>>>>       if (err) {
>>>>         dev_err(&pdev->dev, "Adapter reset failed (%d). Please reboot\n", err);
>>>>         return err;
>>>>       }
>>>>       dev->flags &= ~QLCNIC_NEED_FLR;
>>>>     }
>>> Thanks Bjorn,
>>>
>>> that is very helpful.
>>>
>>> I think that in order to move to option #1 some information would be needed
>>> from those familiar with the device(s). As it is a more invasive change -
>>> pci_reset_function -> pcie_flr.
>>>
>>> So my feeling is that, in lieu of such feedback, option #2 is a good
>>> improvement on the current code.
>>>
>>> OTOH, this driver is 'Supported' as opposed to 'Maintained'.
>>> So perhaps we can just use our best judgement and go for option #1.
>> So, it looks like option #2 is the safest choice as we do reset only if FLR
>> is needed (when pci_reset_function() makes sense)
>>
>> If all agree with that I'll re-send the path
> Yes. Maybe wait 24h, and if there is no further feedback go ahead with that
> plan?
Ok, will do so. Thanks!