Re: Bisected, with rfc/patch - was Re: BUG: unable to handle kernel NULL pointer dereference at sysfs_do_create_link_sd (after mdadm)

[Christoph Hellwig <hch@lst.de>]

On Thu, Apr 23, 2015 at 06:03:14PM +1000, NeilBrown wrote:
> On Thu, 23 Apr 2015 09:37:24 +0200 Christoph Hellwig <hch@lst.de> wrote:
> 
> > Plase fix your device name lifetimes.
> 
> Any chance you could be more explicit?
>
> The commit you identified doesn't seem to help much - md and dm are quite
> different in this area.
> 
> It seems that it is no longer safe to call 'add_disk' between calling
> 'del_gendisk' and bdi_destroy being called.  How can I find out if I am in
> that window, or wait for bdi_destroy to be called?

The bdi is only around if the device is open, either through a device
node, or through a blkdev_get from a file system.  If you get duplicate
names that means you're trying to allocate a new gendisk while the old
one is still around.

In theory you're fine once the device gets ->release called.

Except that we can hold sysfs reference to the qeue, eww.  So for now
try to follow the dm model, but I'll need to add a callback to the
queue called once the request_queue actually is released for this.