Re: [PATCH 06/15] genhd: Add return code to device_add_disk

Fam Zheng
2016-08-17T09:14:22Z

On Wed, 08/17 11:06, Cornelia Huck wrote:
> On Wed, 17 Aug 2016 16:48:23 +0800
> Fam Zheng <famz@redhat.com> wrote:
>
> > On Wed, 08/17 10:49, Cornelia Huck wrote:
> > > On Wed, 17 Aug 2016 15:15:06 +0800
> > > Fam Zheng <famz@redhat.com> wrote:
> > >
> > > > @@ -613,10 +614,8 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
> > > > disk->flags |= GENHD_FL_UP;
> > > >
> > > > retval = blk_alloc_devt(&disk->part0, &devt);
> > > > - if (retval) {
> > > > - WARN_ON(1);
> > > > - return;
> > > > - }
> > > > + if (retval)
> > > > + goto fail;
> > > > disk_to_dev(disk)->devt = devt;
> > > >
> > > > /* ->major and ->first_minor aren't supposed to be
> > > > @@ -625,16 +624,26 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
> > > > disk->major = MAJOR(devt);
> > > > disk->first_minor = MINOR(devt);
> > > >
> > > > - disk_alloc_events(disk);
> > > > + retval = disk_alloc_events(disk);
> > > > + if (retval)
> > > > + goto fail;
> > > >
> > > > /* Register BDI before referencing it from bdev */
> > > > bdi = &disk->queue->backing_dev_info;
> > > > - bdi_register_owner(bdi, disk_to_dev(disk));
> > > > + retval = bdi_register_owner(bdi, disk_to_dev(disk));
> > > > + if (retval)
> > > > + goto fail;
> > > >
> > > > - blk_register_region(disk_devt(disk), disk->minors, NULL,
> > > > - exact_match, exact_lock, disk);
> > > > - register_disk(parent, disk);
> > > > - blk_register_queue(disk);
> > > > + retval = blk_register_region(disk_devt(disk), disk->minors, NULL,
> > > > + exact_match, exact_lock, disk);
> > > > + if (retval)
> > > > + goto fail;
> > > > + retval = register_disk(parent, disk);
> > > > + if (retval)
> > > > + goto fail;
> > > > + retval = blk_register_queue(disk);
> > > > + if (retval)
> > > > + goto fail;
> > > >
> > > > /*
> > > > * Take an extra ref on queue which will be put on disk_release()
> > > > @@ -644,10 +653,20 @@ void device_add_disk(struct device *parent, struct gendisk *disk)
> > > >
> > > > retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
> > > > "bdi");
> > > > + if (retval)
> > > > + goto fail;
> > > > +
> > > > + retval = disk_add_events(disk);
> > > > + if (retval)
> > > > + goto fail;
> > > > +
> > > > + retval = blk_integrity_add(disk);
> > > > + if (retval)
> > > > + goto fail;
> > > > + return 0;
> > > > +fail:
> > > > WARN_ON(retval);
> > > > -
> > > > - disk_add_events(disk);
> > > > - blk_integrity_add(disk);
> > > > + return retval;
> > > > }
> > >
> > > Noticed this when trying to figure out whether the error handling in
> > > virtio_blk was correct:
> > >
> > > Shouldn't you try to cleanup/rewind so that any structures are in a
> > > sane state after failure? The caller doesn't know where device_add_disk
> > > failed, and calling del_gendisk unconditionally like virtio_blk does is
> > > probably not the right thing to do (at the very least, I don't think
> > > unregistering a device that has not been registered is likely to work).
> > >
> >
> > Yes, I think all callers need to be reviewed before device_add_disk do the
> > clean up on error. For this patchset I wanted to keep the change small.
>
> But do the callers even have a chance to do this correctly right now?
> They will either clean up too much, or too little. ('Too little' is
> probably the more common case, given that you just added error
> propagation...)

Right, which is pre-exising.

>
> Can you make del_gendisk handle devices partially setup via
> device_add_disk in all cases? Then you could mandate pairing
> device_add_disk with del_gendisk in all cases, error or not, and you
> should have a better chance on avoiding introducing new errors.
>

Of course, the plan is to write patches on top. I'm not cleaning up anything
here because I'm concerned callers may double free (and I didn't look hard into
that).

Fam