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

["Stojaczyk, Dariusz" <dariusz.stojaczyk@intel.com>]

> -----Original Message-----
> From: Gaëtan Rivet [mailto:gaetan.rivet@6wind.com]
> Sent: Thursday, November 22, 2018 10:54 AM
> To: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>
> Cc: dev@dpdk.org; thomas@monjalon.net
> Subject: Re: [PATCH v2] dev: don't remove devargs that are still referenced
> 
> 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.

Ack, I'll do that.

> 
> > +		return ret;
> >  	}
> >
> >  	*new_dev = dev;
> > --
> > 2.17.1
> >
> 
> --
> Gaëtan Rivet
> 6WIND