[dpdk-stable] [dpdk-dev] [PATCH v3] dev: don't remove devargs that are still referenced

[Kevin Traynor]

On 11/27/2018 01:03 PM, Stojaczyk, Dariusz wrote:
> 
> 
>> -----Original Message-----
>> From: Kevin Traynor [mailto:ktraynor at redhat.com]
>> Sent: Tuesday, November 27, 2018 12:40 PM
>> To: Stojaczyk, Dariusz <dariusz.stojaczyk at intel.com>; Maxime Coquelin
>> <maxime.coquelin at redhat.com>
>> Cc: gaetan.rivet at 6wind.com; thomas at monjalon.net; stable at dpdk.org
>> Subject: Re: [dpdk-dev] [PATCH v3] dev: don't remove devargs that are still
>> referenced
>>
>> On 11/23/2018 09:45 PM, Stojaczyk, Dariusz wrote:
>>>
>>>
>>>> -----Original Message-----
>>>> From: Maxime Coquelin [mailto:maxime.coquelin at redhat.com]
>>>> Sent: Friday, November 23, 2018 6:05 PM
>>>> To: Stojaczyk, Dariusz <dariusz.stojaczyk at intel.com>; dev at dpdk.org
>>>> Cc: gaetan.rivet at 6wind.com; thomas at monjalon.net
>>>> Subject: Re: [dpdk-dev] [PATCH v3] dev: don't remove devargs that are
>> still
>>>> referenced
>>>>
>>>> Hi,
>>>>
>>>> On 11/23/18 4:43 PM, Darek Stojaczyk wrote:
>>>>> Even if a device failed to plug, it's still a device
>>>>> object that references the devargs. Those devargs will
>>>>> be freed automatically together with the device, but
>>>>> freeing them any earlier - like it's done in the hotplug
>>>>> error handling path right now - will give us a dangling
>>>>> pointer and a segfault scenario.
>>>>>
>>>>> Consider the following case:
>>>>>   * secondary process receives the hotplug request IPC message
>>>>>     * devargs are either created or updated
>>>>>     * the bus is scanned
>>>>>       * a new device object is created with the latest devargs
>>>>>     * the device can't be plugged for whatever reason,
>>>>>       bus->plug returns error
>>>>>       * the devargs are freed, even though they're still referenced
>>>>>         by the device object on the bus
>>>>>
>>>>> For PCI devices, the generic device name comes from
>>>>> a buffer within the devargs. Freeing those will make
>>>>> EAL segfault whenever the device name is checked.
>>>>>
>>>>> This patch just prevents the hotplug error handling
>>>>> path from removing the devargs when there's a device
>>>>> that references them. This is done by simply exiting
>>>>> early from the hotplug function. As mentioned in the
>>>>> beginning, those devargs will be freed later, together
>>>>> with the device itself.
>>>>>
>>>>> Fixes: 7e8b26650146 ("eal: fix hotplug add / remove")
>>>>
>>>> Should you also cc stable?
>>>> Above commit is in since v17.08.
>>>>
>>>
>>> Hi Maxime,
>>>
>>> Stable could use a similar patch, but not exactly this one as it is now. I'll
>> resubmit for stable once the one here gets approved.
>>>
>>
>> Hi Darek, feel free to send patch to stable at dpdk.org with [18.08]
>> subject prefix, now that this is applied on master, thanks.
> 
> Kevin, I just tried rebasing this patch on 18.08, but the relevant code in 18.08 is just too much of a mess and I prefer not to touch it.

No, problem, thanks for checking it,
Kevin.

> Sorry,
> D.
> 
>>
>>
>>> Thank you,
>>> D.
>>>
>>>>> Cc: gaetan.rivet at 6wind.com
>>>>> Cc: thomas at monjalon.net
>>>>>
>>>>> Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk at intel.com>
>>>>> ---
>>>>> Changes since v2:
>>>>>   * added an extra comment (Gaetan)
>>>>>
>>>>> Changes since v1:
>>>>>   * described the failing scenario in commit msg (Thomas)
>>>>>
>>>>>   lib/librte_eal/common/eal_common_dev.c | 13 ++++++++-----
>>>>>   1 file changed, 8 insertions(+), 5 deletions(-)
>>>>>
>>>>> diff --git a/lib/librte_eal/common/eal_common_dev.c
>>>> b/lib/librte_eal/common/eal_common_dev.c
>>>>> index 1fdc9ab17..d7950bc9a 100644
>>>>> --- a/lib/librte_eal/common/eal_common_dev.c
>>>>> +++ b/lib/librte_eal/common/eal_common_dev.c
>>>>> @@ -166,14 +166,17 @@ local_dev_probe(const char *devargs, struct
>>>> rte_device **new_dev)
>>>>>   		ret = -ENODEV;
>>>>>   		goto err_devarg;
>>>>>   	}
>>>>> +	/* Since there is a matching device, it is now its responsibility
>>>>> +	 * to manage the devargs we've just inserted. From this point
>>>>> +	 * those devargs shouldn't be removed manually anymore.
>>>>> +	 */
>>>>>
>>>>>   	ret = dev->bus->plug(dev);
>>>>>   	if (ret) {
>>>>> -		if (rte_dev_is_probed(dev)) /* if already succeeded earlier
>>>> */
>>>>> -			return ret; /* no rollback */
>>>>> -		RTE_LOG(ERR, EAL, "Driver cannot attach the device (%s)\n",
>>>>> -			dev->name);
>>>>> -		goto err_devarg;
>>>>> +		if (!rte_dev_is_probed(dev)) /* if hasn't succeeded earlier */
>>>>> +			RTE_LOG(ERR, EAL, "Driver cannot attach the device
>>>> (%s)\n",
>>>>> +				dev->name);
>>>>> +		return ret;
>>>>>   	}
>>>>>
>>>>>   	*new_dev = dev;
>>>>>
>>>>
>>>> Other than that, it looks good to me:
>>>> Acked-by: Maxime Coquelin <maxime.coquelin at redhat.com>
>>>>
>>>> Regards,
>>>> Maxime
>