netdev - Re: [PATCH v4 3/3] IB/ipoib: Log sysfs 'dev

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Message-ID: <4dbef82e363766ab81cd7371df1e1f3b1e0a6af5.camel@redhat.com>
Date:   Thu, 13 Sep 2018 11:45:57 -0400
From:   Doug Ledford <dledford@...hat.com>
To:     Arseny Maslennikov <ar@...msu.ru>, Jason Gunthorpe <jgg@...pe.ca>
Cc:     linux-rdma@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v4 3/3] IB/ipoib: Log sysfs 'dev_id' accesses from
 userspace

On Sun, 2018-09-09 at 23:55 +0300, Arseny Maslennikov wrote:
> On Sun, Sep 09, 2018 at 09:11:46PM +0300, Arseny Maslennikov wrote:
> > On Fri, Sep 07, 2018 at 09:43:59AM -0600, Jason Gunthorpe wrote:
> > > On Thu, Sep 06, 2018 at 05:51:12PM +0300, Arseny Maslennikov wrote:
> > > > Some tools may currently be using only the deprecated attribute;
> > > > let's print an elaborate and clear deprecation notice to kmsg.
> > > > 
> > > > To do that, we have to replace the whole sysfs file, since we inherit
> > > > the original one from netdev.
> > > > 
> > > > Signed-off-by: Arseny Maslennikov <ar@...msu.ru>
> > > >  drivers/infiniband/ulp/ipoib/ipoib_main.c | 31 +++++++++++++++++++++++
> > > >  1 file changed, 31 insertions(+)
> > > > 
> > > > diff --git a/drivers/infiniband/ulp/ipoib/ipoib_main.c b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > > index 30f840f874b3..74732726ec6f 100644
> > > > +++ b/drivers/infiniband/ulp/ipoib/ipoib_main.c
> > > > @@ -2386,6 +2386,35 @@ int ipoib_add_pkey_attr(struct net_device *dev)
> > > >  	return device_create_file(&dev->dev, &dev_attr_pkey);
> > > >  }
> > > >  
> > > > +/*
> > > > + * We erroneously exposed the iface's port number in the dev_id
> > > > + * sysfs field long after dev_port was introduced for that purpose[1],
> > > > + * and we need to stop everyone from relying on that.
> > > > + * Let's overload the shower routine for the dev_id file here
> > > > + * to gently bring the issue up.
> > > > + *
> > > > + * [1] https://www.spinics.net/lists/netdev/msg272123.html
> > > > + */
> > > > +static ssize_t dev_id_show(struct device *dev,
> > > > +			   struct device_attribute *attr, char *buf)
> > > > +{
> > > > +	struct net_device *ndev = to_net_dev(dev);
> > > > +
> > > > +	if (ndev->dev_id == ndev->dev_port)
> > > > +		netdev_info_once(ndev,
> > > > +			"\"%s\" wants to know my dev_id. Should it look at dev_port instead? See Documentation/ABI/testing/sysfs-class-net for more info.\n",
> > > > +			current->comm);
> > > > +
> > > > +	return sprintf(buf, "%#x\n", ndev->dev_id);
> > > > +}
> > > > +static DEVICE_ATTR_RO(dev_id);
> > > > +
> > > > +int ipoib_intercept_dev_id_attr(struct net_device *dev)
> > > > +{
> > > > +	device_remove_file(&dev->dev, &dev_attr_dev_id);
> > > > +	return device_create_file(&dev->dev, &dev_attr_dev_id);
> > > > +}
> > > 
> > > Isn't this racey with userspace? Ie what happens if udev is querying
> > > the dev_id right here?
> > 
> > udev in particular does not use dev_id at all since 2014, because "why
> > would we keep using dev_id if it is not the right thing to use?".
> > 
> > > 
> > > Do we know there is no userspace doing this?
> > > 
> > 
> > Not for sure.
> > 
> > If we move all the sysfs handling stuff we introduce in _add_port():
> >  - pkey
> >  - umcast
> >  - {create,delete}_child
> >  - connected/datagram mode
> > to _ndo_init(), which is called by register_netdev before it sends
> > the netlink message, would that suffice to eliminate the race?
> > (Sysfs files for {create,delete}_child go to _parent_init() then).
> > 
> 
> No, we can't, sorry for the noise. ndo_init() runs before the kobject
> becomes available.
> 
> Anyway, our sysfs attributes being racy is unrelated to the patch series
> subject, and I can't come up with any other ideas what to do with them
> that do not involve adjustments to register_netdev.

Agreed (that fixing the race issues is a different patch series).

-- 
Doug Ledford <dledford@...hat.com>
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