Re: [dpdk-dev] [PATCH v2] dev: don't remove devargs that are still referenced

["Gaëtan Rivet" <gaetan.rivet@6wind.com>]

On Wed, Nov 21, 2018 at 08:38:27PM +0100, 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.
> 

This seems ok in conjunction with Thomas' patch on overwriting devargs
on insertion.

The only place a device will be freed is the unplug bus ops, it already
does remove the device devargs.

> Fixes: 7e8b26650146 ("eal: fix hotplug add / remove")
> Cc: gaetan.rivet@6wind.com
> Cc: thomas@monjalon.net
> 
> Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@intel.com>
> ---
>  lib/librte_eal/common/eal_common_dev.c | 9 ++++-----
>  1 file changed, 4 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..b6fc5e437 100644
> --- a/lib/librte_eal/common/eal_common_dev.c
> +++ b/lib/librte_eal/common/eal_common_dev.c
> @@ -169,11 +169,10 @@ local_dev_probe(const char *devargs, struct rte_device **new_dev)
>  
>  	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);

Maybe a comment here to describe that the devargs is still the
responsibility of the rte_device and should not be removed.

> +		return ret;
>  	}
>  
>  	*new_dev = dev;
> -- 
> 2.17.1
> 

-- 
Gaëtan Rivet
6WIND