Re: [PATCH 17/19] fs: Reduce inode I_FREEING and factor inode disposal

Sage Weil
2010-10-18T21:24:12Z

Hi guys,

I'm a bit late the party, but:

On Sun, 17 Oct 2010, Dave Chinner wrote:
> On Sun, Oct 17, 2010 at 04:13:10PM +1100, Nick Piggin wrote:
> > On Sun, Oct 17, 2010 at 03:35:14PM +1100, Nick Piggin wrote:
> > > On Sun, Oct 17, 2010 at 03:13:13PM +1100, Dave Chinner wrote:
> > > > On Sun, Oct 17, 2010 at 01:49:23PM +1100, Nick Piggin wrote:
> > > > > On Sat, Oct 16, 2010 at 09:30:47PM -0400, Christoph Hellwig wrote:
> > > > > > > * inode->i_lock is *always* the innermost lock.
> > > > > > > *
> > > > > > > + * inode->i_lock is *always* the innermost lock.
> > > > > > > + *
> > > > > >
> > > > > > No need to repeat, we got it..
> > > > >
> > > > > Except that I didn't see where you fixed all the places where it is
> > > > > *not* the innermost lock. Like for example places that take dcache_lock
> > > > > inside i_lock.
> > > >
> > > > I can't find any code outside of ceph where the dcache_lock is used
> > > > within 200 lines of code of the inode->i_lock. The ceph code is not
> > > > nesting them, though.
> > >
> > > You mustn't have looked very hard? From ceph:
> > >
> > > spin_unlock(&dcache_lock);
> > > spin_unlock(&inode->i_lock);
> > >
> > > (and yes, acquisition side does go in i_lock->dcache_lock order)
>
> Sorry, easy to miss with a quick grep when the locks are taken in
> different functions.
>
> Anyway, this one looks difficult to fix without knowing something
> about Ceph and wtf it is doing there. It's one to punt to the
> maintainer to solve as it's not critical to this patch set.

I took a look at this code and was able to remove the i_lock ->
dcache_lock nesting. To be honest, I'm not sure why I did it that way in
the first place. The only point (now) where i_lock is used/needed is
while checking the ceph inode flags, and that's done without holding
dcache_lock (presumably soon to be d_lock).

The patch is 622386be in the for-next branch of
git://git.kernel.org/pub/scm/linux/kernel/git/sage/ceph-client.git

Anyway, hope this helps!
sage