[PATCH] fs/block_dev.c: Use hd_part to find block inodes

[Keith Busch]

On Fri, 22 Aug 2014, Keith Busch wrote:
> On Fri, 22 Aug 2014, Christoph Hellwig wrote:
>> On Fri, Aug 22, 2014 at 10:28:16AM -0600, Keith Busch wrote:
>>> When using the GENHD_FL_EXT_DEVT disk flags, a newly added device may
>>> be assigned the same major/minor as one that was previously removed but
>>> opened, and the pesky userspace refuses to close it!
>> 
>> Which means life time rules for those dev_t allocations are broken.
>> Please fix it to not release the dev_t until the device isn't referenced
>> at all.
>
> Okay, thanks. So a proper fix would not let extended devt minors get
> reused while still referenced, so we can't release it unconditionally
> from del_gendisk(). I think the following does that, but I had to add
> a reference counter to gendisk.

Sorry for the rapid churn; I hadn't followed the function pointers through
to discover the correct place to release the devt. This one's much simpler:
---
diff --git a/block/genhd.c b/block/genhd.c
index 791f419..321f1fd 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -665,7 +665,6 @@ void del_gendisk(struct gendisk *disk)
  		sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
  	pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
  	device_del(disk_to_dev(disk));
-	blk_free_devt(disk_to_dev(disk)->devt);
  }
  EXPORT_SYMBOL(del_gendisk);

@@ -1098,6 +1097,7 @@ static void disk_release(struct device *dev)
  {
  	struct gendisk *disk = dev_to_disk(dev);

+	blk_free_devt(dev->devt);
  	disk_release_events(disk);
  	kfree(disk->random);
  	disk_replace_part_tbl(disk, NULL);
--