Re: [PATCH] Per-superblock unused dentry LRU lists V2

[Balbir Singh <balbir@in.ibm.com>]

> 
> FWIW, this create/unlink load has been triggering reliable "Busy
> inodes after unmount" errors that I've slowly been tracking down.
> After I fixed the last problem in XFS late last week, I've
> been getting a failure that i think is the unmount/prune_dcache
> races that you and Neil have recently fixed.

Good, we were not able to reproduce the problem and test the fix.
I guess we have a more reliable way of testing the fix now.

> 
> Basically, I'm seeing a transient elevated reference  count on
> the root inode of the XFS filesystem during the final put_super()
> in generic_shutdown_super(). If I trigger a BUG_ON() when that
> elevated reference count is detected, byt he time al the cpus
> are stopped and I'm in kdb, the reference count on the root inode
> is only 1. The next thing I was going to track was where the dentry
> for the root inodes was.

The dput() would happen eventually, in this case after the umount.
kprobes might be more reliable for extracting information in this
case. 

> 
> I'll know if this really is the same race soon, as the create/unlink
> test would trip it under an hour.....
> 
> Cheers,
> 
> Dave.

	Cheers,
	Balbir Singh,
	Linux Technology Center,
	IBM Software Labs