linux-kernel - Re: [PATCH v3 3/4] cxl/mem: Do not rely on device_add() side effects for dev_set

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Date:   Wed, 31 Mar 2021 09:04:32 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     linux-cxl@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        "Schofield, Alison" <alison.schofield@...el.com>
Subject: Re: [PATCH v3 3/4] cxl/mem: Do not rely on device_add() side effects
 for dev_set_name() failures

On Wed, Mar 31, 2021 at 6:10 AM Jason Gunthorpe <jgg@...dia.com> wrote:
>
> On Tue, Mar 30, 2021 at 04:36:42PM -0700, Dan Williams wrote:
> > +static int cxl_mem_add_memdev(struct cxl_mem *cxlm)
> > +{
> > +     struct cxl_memdev *cxlmd;
> > +     struct device *dev;
> > +     struct cdev *cdev;
> > +     int rc;
> > +
> > +     cxlmd = cxl_memdev_alloc(cxlm);
> > +     if (IS_ERR(cxlmd))
> > +             return PTR_ERR(cxlmd);
> > +
> > +     dev = &cxlmd->dev;
> > +     rc = dev_set_name(dev, "mem%d", cxlmd->id);
> > +     if (rc)
> > +             goto err;
> >
> > +     cdev = &cxlmd->cdev;
> >       cxl_memdev_activate(cxlmd, cxlm);
> >       rc = cdev_device_add(cdev, dev);
> >       if (rc)
> > -             goto err_add;
> > +             goto err;
>
> It might read nicer to have the error unwind here just call cxl_memdev_unregister()

Perhaps, but I don't think cdev_del() and device_del() are prepared to
deal with an object that was not successfully added.

>
> > -     return devm_add_action_or_reset(&pdev->dev, cxl_memdev_unregister,
> > +     return devm_add_action_or_reset(dev->parent, cxl_memdev_unregister,
> >                                       cxlmd);
>
> Since that is what the error unwind does at this point.

Right, but at this point the code knows that cdev_del() and
device_del() will receive an object in the appropriate state.

>
> >
> > -err_add:
> > +err:
> >       /*
> >        * The cdev was briefly live, shutdown any ioctl operations that
> >        * saw that state.
> >        */
> >       cxl_memdev_shutdown(cxlmd);
>
> Then this doesn't need to be a function
>
> But it is OK as is

Unless I'm missing something I think it's required to use only
put_device() to cleanup after cdev_device_add() failure, but yes I
don't like that cxl_memdev_shutdown() needs to be open coded like
this.

>
> Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Appreciate it.