Re: frequent softlockups with 3.10rc6.

[Al Viro <viro@ZenIV.linux.org.uk>]

On Thu, Jun 27, 2013 at 10:22:45PM -1000, Linus Torvalds wrote:

> > It looks ok, but I still think it is solving the wrong problem.
> > FWIW, your optimisation has much wider application that just this
> > one place. I'll have a look to see how we can apply this approach
> > across all the inode lookup+validate code we currently have that
> > unconditionally takes the inode->i_lock....
> 
> Yes, I was looking at all the other cases that also seemed to be
> testing i_state for those "about to go away" cases.

FWIW, there's a subtle issue here - something like ext2_new_inode()
starts with allocating an inode and putting it into list (no I_NEW
yet), then decides what inumber will it have and calls insert_inode_locked(),
which sets I_NEW.  Then we proceed with initializing the inode (and
eventually do unlock_new_inode(), which removes I_NEW).  We depend on having
no pages in the pagecache of that sucker prior to insert_inode_locked() call;
you really don't want to start playing with writeback on this half-initialized
in-core inode.