Re: [PATCH 1/2] block: grab a device refcount in disk_uevent

[Christoph Hellwig <hch@lst.de>]

On Thu, Jul 01, 2021 at 04:54:05PM +0800, Ming Lei wrote:
> On Thu, Jul 01, 2021 at 10:16:37AM +0200, Christoph Hellwig wrote:
> > Sending uevents requires the struct device to be alive.  To
> > ensure that grab the device refcount instead of just an inode
> > reference.
> > 
> > Fixes: bc359d03c7ec ("block: add a disk_uevent helper")
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  block/genhd.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/block/genhd.c b/block/genhd.c
> > index 79aa40b4c39c..af4d2ab4a633 100644
> > --- a/block/genhd.c
> > +++ b/block/genhd.c
> > @@ -365,12 +365,12 @@ void disk_uevent(struct gendisk *disk, enum kobject_action action)
> >  	xa_for_each(&disk->part_tbl, idx, part) {
> >  		if (bdev_is_partition(part) && !bdev_nr_sectors(part))
> >  			continue;
> > -		if (!bdgrab(part))
> > +		if (!kobject_get_unless_zero(&part->bd_device.kobj))
> >  			continue;
> 
> ->bd_device is embedded in the block device, and it has same lifetime
> with the block device, even part_release() calls bdput() to release this
> device, so why doesn't work by holding a inode reference?

Because sending a uevent on a device that has device_del called on it
is going to blow up.