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From: Dan Williams <dan.j.williams@intel.com>
Date: Wed, 5 Feb 2020 10:23:00 -0800
Message-ID: <CAPcyv4itFypOmv38Oo=DRWk_1Y3PFhPpYPDzxShmZVY9ZsTNLA@mail.gmail.com>
Subject: Re: [bug report] libnvdimm, nvdimm: dimm driver and base libnvdimm
 device-driver infrastructure
To: Dan Carpenter <dan.carpenter@oracle.com>
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On Wed, Feb 5, 2020 at 10:11 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
>
> On Wed, Feb 05, 2020 at 09:47:01AM -0800, Dan Williams wrote:
> > On Wed, Feb 5, 2020 at 4:38 AM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> > >
> > > Hello Dan Williams,
> > >
> > > The patch 4d88a97aa9e8: "libnvdimm, nvdimm: dimm driver and base
> > > libnvdimm device-driver infrastructure" from May 31, 2015, leads to
> > > the following static checker warning:
> > >
> > >         drivers/nvdimm/bus.c:511 nd_async_device_register()
> > >         error: dereferencing freed memory 'dev'
> > >
> > > drivers/nvdimm/bus.c
> > >    502  static void nd_async_device_register(void *d, async_cookie_t cookie)
> > >    503  {
> > >    504          struct device *dev = d;
> > >    505
> > >    506          if (device_add(dev) != 0) {
> > >    507                  dev_err(dev, "%s: failed\n", __func__);
> > >    508                  put_device(dev);
> > >                         ^^^^^^^^^^^^^^^
> > >    509          }
> > >    510          put_device(dev);
> > >                 ^^^^^^^^^^^^^^
> > >    511          if (dev->parent)
> > >    512                  put_device(dev->parent);
> > >    513  }
> > >
> > > We call get_device() from __nd_device_register(), I guess.  It seems
> > > buggy to call put device twice on error.
> >
> > The registration path does:
> >
> >         get_device(dev);
> >
> >         async_schedule_dev_domain(nd_async_device_register, dev,
> >                                   &nd_async_domain);
> >
> > ...and device_add() does its own get_device().
>
> device_add() does its own put_device() at the end so it's a net zero.
>

It does it's own, yes, but the put_device() after device_add() failure
is there to drop the reference taken by device_initialize().
Otherwise, device_add() has always documented:

 * NOTE: _Never_ directly free @dev after calling this function, even
 * if it returned an error! Always use put_device() to give up your
 * reference instead.

...so what am I missing?
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