netdev - Re: [PATCH net] bnx2x: don't reset chip on cleanup if PCI function is offline

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Message-Id: <57AB2C11.1070706@linux.vnet.ibm.com>
Date:	Wed, 10 Aug 2016 10:28:49 -0300
From:	"Guilherme G. Piccoli" <gpiccoli@...ux.vnet.ibm.com>
To:	Yuval Mintz <Yuval.Mintz@...gic.com>
Cc:	netdev <netdev@...r.kernel.org>,
	Ariel Elior <Ariel.Elior@...gic.com>
Subject: Re: [PATCH net] bnx2x: don't reset chip on cleanup if PCI function is
 offline

On 08/10/2016 04:59 AM, Yuval Mintz wrote:
>>> Why would the published resume()  from pci_error_handlers be called in this
>> scenario?
>>
>> It isn't. That's why I specifically commented on commit message: "There are two
>> cases though that another path is taken on the code".
>>
>> The code path reach bnx2x_chip_cleanup() on device removal from the system,
>> as seen in the below call trace:
>>
>> bnx2x_chip_cleanup+0x3c0/0x910 [bnx2x]
>> bnx2x_nic_unload+0x268/0xaf0 [bnx2x]
>> bnx2x_close+0x34/0x50 [bnx2x]
>> __dev_close_many+0xd4/0x150
>> dev_close_many+0xa8/0x160
>> rollback_registered_many+0x174/0x3f0
>> rollback_registered+0x40/0x70
>> unregister_netdevice_queue+0x98/0x110
>> unregister_netdev+0x34/0x50
>> __bnx2x_remove+0xa8/0x3a0 [bnx2x]
>> pci_device_remove+0x70/0x110
>
> Makes sense.
>
>>>> Also, we avoid the MCP information dump in case of non-recoverable
>>>> PCI error (when adapter is about to be removed), since it will certainly fail.
>>>
>>> We should probably avoid several things here; Why specifically only this?
>>
>> For example, we shouldn't execute bnx2x_timer() in this scenario. But I thought
>> it'd be too much to check every call of a timer function against PCI channel state
>> just to avoid it's execution on this scenario, so I just let it execute, since it seems
>> harmless.
>>
>>>> +	/* Reset the chip, unless PCI function is offline. If we reach this
>>>> +	 * point following a PCI error handling, it means device is really
>>>> +	 * in a bad state and we're about to remove it, so reset the chip
>>>> +	 * is not a good idea.
>>>> +	 */
>>>> +	if (!pci_channel_offline(bp->pdev)) {
>>>> +		rc = bnx2x_reset_hw(bp, reset_code);
>>>> +		if (rc)
>>>> +			BNX2X_ERR("HW_RESET failed\n");
>>>> +	}
>>>
>>> Why not simply check this at the beginning of the function?
>>
>> Because I wasn't sure if I could drop the entire execution of chip_cleanup(). I
>> tried to keep the most of this function aiming to shutdown the module in a
>> gentle way, like cleaning MAC, stopping queues...but again, I'm open to
>> suggestions and gladly will change this in v2 if you think it's for the best.
>
> Problem is I won't be able to have a more thorough review of this in the next
> couple of days - and other than code-review I won't have a reasonable way
> of testing this [I can use aer_inject, but I don't have your magical EEH
> error injections, and I'm not at all certain it would suffice for a good testing ].
>
> I agree that even as-is, what you're suggesting is an improvement to the
> existing flow - so it's basically up to dave, i.e., whether to take a half fix
> or wait for a more thorough one.
>

Thanks for your consideration. The point is: the important part of this 
patch is avoiding the reset_hw() path, since it will clearly fail and 
generate soft lockups. This is the fix per se, the other part (regarding 
the MCP dump) is just an improvement; surely we have more potential 
improvements to explore, but they wouldn't be fixes, only code improvements.

So, I wouldn't call this a half fix, but yet, a completely fix with a 
small improvement as a bonus :)

Cheers,


Guilherme