2.6.28-rc2: (mtd)block/partitions BUG with kobject reference count

[Kay Sievers]

On Thu, Oct 30, 2008 at 22:51, Kay Sievers <kay.sievers at vrfy.org> wrote:
> On Thu, Oct 30, 2008 at 00:28, Peter Korsgaard <jacmet at sunsite.dk> wrote:
>>>>>>> "Rafael" == Rafael J Wysocki <rjw at sisk.pl> writes:
>>
>>  Rafael> On Wednesday, 29 of October 2008, Peter Korsgaard wrote:
>>  >> Hi,
>>  >>
>>  >> I'm seing what looks like a kobject reference count issue with
>>  >> mtdblock_ro + mtd_dataflash + mtd partitions and repeated unbind/bind.
>>  >> I'm on 2.6.28-rc2, but I can reproduce the problem on 2.6.27 as well.
>>
>>  Rafael> Is it reproducible with 2.6.26 too?
>>
>> Sorry, I haven't backported my platform support code to such "old"
>> kernel. I can do it though, if you think it will help pinpoint the
>> issue.
>
> This sounds like a possible reason for the problem:
> "After digging into the mtd code, this bug is not related to our driver. It
> should be a subtle bug in mtd core code.
>
> In add_mtd_partition, for 2 partitions, 2 gendisk structures will be
> allocated. But these 2 gendisk->queue will be set to the same
> request_queue. Then when unregistering the 1st partition, from the
> same request_queue->backing_dev_info, the bdi struct will be set to
> NULL. So for the 2nd partition (bdi == NULL), the sysfs dir of 2nd
> partition will not be removed. Finally, when modprobe the module
> again, the 2nd partition won't be added"
> https://blackfin.uclinux.org/gf/tracker/4463

Looks like a bdi issue:
  http://lkml.org/lkml/2008/10/30/519

Peter, if I do this (whitespace mangled, just pasted in here), the
error goes away for me. Can you try this?

Thanks,
Kay

--- a/block/genhd.c
+++ b/block/genhd.c
@@ -515,7 +515,8 @@ void add_disk(struct gendisk *disk)
        blk_register_queue(disk);

        bdi = &disk->queue->backing_dev_info;
-       bdi_register_dev(bdi, disk_devt(disk));
+       if (!bdi->dev)
+               bdi_register_dev(bdi, disk_devt(disk));
        retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
                                   "bdi");
        WARN_ON(retval);