On Fri, 2006-06-30 at 12:31 +0100, David Howells wrote:
> Andrew Morton <[EMAIL PROTECTED]> wrote:
>
> > But why was yum (or an RPM script) dinking with loop and
> > mounting/unmounting things?
>
> It may have restarted the automounter... this may cause mounts and unmounts...
>
> I've done a bit of probing, and when both ext3 and NFS go into the superblock
> squidger with a tree that only has a root dentry, that root dentry has a usage
> count of 1:
>
> ### Shrink root c629b088{1}
> -->shrink_dcache_for_umount_subtree(c629b088)
> - AT c629b088{0}
> - consume c629b088{0}
> ### Shrunk
>
>
> ### Shrink root c621d710{1}
> -->shrink_dcache_for_umount_subtree(c621d710)
> - AT c621d710{0}
> - consume c621d710{0}
> ### Shrunk
>
> But when autofs4 goes in there with a minimal tree:
>
> ### Shrink root c6b714b0{2}
> -->shrink_dcache_for_umount_subtree(c6b714b0)
> - AT c6b714b0{1}
> - consume c6b714b0{1}
> BUG: Dentry c6b714b0{i=1a80,n=/} still in use (1) [unmount of autofs
> autofs]
> ------------[ cut here ]------------
> kernel BUG at fs/dcache.c:618!
>
> It's got a usage count of *2*. That means the root dentry is still in use
> somewhere beyond the superblock s_root reference.
>
> I think this in autofs4_fill_super() is the problem:
>
> /*
> * Take a reference to the root dentry so we get a chance to
> * clean up the dentry tree on umount.
> * See autofs4_force_release.
> */
> sbi->root = dget(root);
>
> autofs4 violates the assumptions that I was told I could make. autofs4
> expects to clean up its dentries in autofs4_put_super(), when it should
> perhaps really be overloading the kill_sb() op and doing it before calling
> kill_anon_super().
Right you are. Sorry.
Looks like I've got a bit of work to do then.
The main reason this exists is that if the daemon is summarily killed
dentrys with a non-zero reference count can be left in the tree so they
need to be culled.
I wish I'd had time to pay more attention to the work your doing David.
A super brief overview would be really helpful if you have the time.
Sounds like all I need to do is move the function. Overloading kill_sb
sounds good. I'll investigate.
I really need to try and motivate myself to do some work on my house
this weekend so it may be a little while before I get back.
Ian
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