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

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

> -----Original Message-----
> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> Sent: Friday, November 23, 2018 6:05 PM
> To: Stojaczyk, Dariusz <dariusz.stojaczyk@intel.com>; dev@dpdk.org
> Cc: gaetan.rivet@6wind.com; thomas@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.

Thank you,
D.  

> > Cc: gaetan.rivet@6wind.com
> > Cc: thomas@monjalon.net
> >
> > Signed-off-by: Darek Stojaczyk <dariusz.stojaczyk@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@redhat.com>
> 
> Regards,
> Maxime