Re: [PATCH 18/18] fs: Reduce inode I_FREEING and factor inode disposal

Dave Chinner
2010-10-08T13:55:41Z

On Fri, Oct 08, 2010 at 01:10:52PM +0100, Al Viro wrote:
> On Fri, Oct 08, 2010 at 09:52:49PM +1100, Dave Chinner wrote:
> > On Fri, Oct 08, 2010 at 11:18:19AM +0100, Al Viro wrote:
> > > On Fri, Oct 08, 2010 at 04:21:32PM +1100, Dave Chinner wrote:
> > >
> > > > + spin_unlock(&sb->s_inodes_lock);
> > > >
> > > > - spin_lock(&inode_lru_lock);
> > > > - list_move(&inode->i_lru, dispose);
> > > > - spin_unlock(&inode_lru_lock);
> > > > + dispose_one_inode(inode);
> > > >
> > > > - percpu_counter_dec(&nr_inodes_unused);
> > > > + spin_lock(&sb->s_inodes_lock);
> > >
> > > And now you've unlocked the list and even blocked. What's going to
> > > keep next valid through that fun?
> >
> > See the comment at the start of the loop in invalidate_list():
> >
> > /*
> > * We can reschedule here without worrying about the list's
> > * consistency because the per-sb list of inodes must not
> > * change during umount anymore, and because iprune_sem keeps
> > * shrink_icache_memory() away.
> > */
> > cond_resched_lock(&sb->s_inodes_lock);
> >
> > Hence I've assumed it's ok to add another point that drops locks and blocks
> > inside the loop and next will still be valid.
>
> I'm not convinced, TBH; IOW, the original might have been broken by that.
> The trouble is, this function is called not only on umount(). Block device
> invalidation paths also can lead to it.

Yeah, I see that now. Thanks for pointing it out.

> Moreover, even for umount-only
> side of things, remember that there's fsnotify as well.

I thought that the fsnotify_unmount_inodes() cleaned everything up
before we called invalidate_list().

> Original code
> did _everything_ except the actual dropping inodes without releasing
> inode_lock. I'm not saying that change is broken (or, in case of
> non-umount paths, makes breakage worse), but I'd like to see more analysis
> of that area.

I think I'll avoid the whole issue right now by not making this
change to invalidate_list()....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com