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

[Kevin Traynor]

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.


> 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