Re: [patch 29/52] fs: icache lock i_count

Nick Piggin
2010-06-30T14:33:09Z

On Wed, Jun 30, 2010 at 05:27:02PM +1000, Dave Chinner wrote:
> On Thu, Jun 24, 2010 at 01:02:41PM +1000, npiggin@suse.de wrote:
> > Protect inode->i_count with i_lock, rather than having it atomic.
> > Next step should also be to move things together (eg. the refcount increment
> > into d_instantiate, which will remove a lock/unlock cycle on i_lock).
> .....
> > Index: linux-2.6/fs/inode.c
> > ===================================================================
> > --- linux-2.6.orig/fs/inode.c
> > +++ linux-2.6/fs/inode.c
> > @@ -33,14 +33,13 @@
> > * inode_hash_lock protects:
> > * inode hash table, i_hash
> > * inode->i_lock protects:
> > - * i_state
> > + * i_state, i_count
> > *
> > * Ordering:
> > * inode_lock
> > * sb_inode_list_lock
> > * inode->i_lock
> > - * inode_lock
> > - * inode_hash_lock
> > + * inode_hash_lock
> > */
>
> I thought that the rule governing the use of inode->i_lock was that
> it can be used anywhere as long as it is the innermost lock.
>
> Hmmm, no references in the code or documentation. Google gives a
> pretty good reference:
>
> http://www.mail-archive.com/linux-ext4@vger.kernel.org/msg02584.html
>
> Perhaps a different/new lock needs to be used here?

Well I just changed the order (and documented it to boot :)). It's
pretty easy to verify that LOR is no problem. inode hash is only
taken in a very few places so other code outside inode.c is fine to
use i_lock as an innermost lock.