Re: [GIT PULL] Please pull NFS client bugfixes....

[Peter Zijlstra <peterz@infradead.org>]

On Thu, 2010-01-07 at 18:00 -0800, Linus Torvalds wrote:
> 
> On Thu, 7 Jan 2010, Linus Torvalds wrote:
> > 
> > You cannot mmap a directory (and you can't readdir a non-directory), so if 
> > it's a per-inode NFS lock, then the simplest fix _might_ be to just put 
> > directory locks in a different lockdep class from non-directory locks. 
> > That might fix it.
> > 
> > Of course, if it's not a per-inode lock, that doesn't help.
> 
> Hmm. I notice that we already do this in unlock_new_inode() for i_mutex. 
> And I googled for the problem, and it does indeed seem to be about the 
> normal i_mutex <-> mmap_sem thing with filldir-vs-mmap.
> 
> Is there perhaps some path where NFS creates new inodes without going 
> through the normal path? Like the root inode or something? So then you'd 
> have a root inode with i_mutex annotated as being in the same class as a 
> regular file, which completes the lockdep chain.

Quite possible, but I got lost trying to find anything like the root
inode.

> Or maybe there is something else I'm missing.
> 
> I'm adding Peter and Ingo to the Cc as the "lockdep guys". Maybe they see 
> what I am missing.

Not really, nfs_fhget() seems to know about directories as it has a
S_ISDIR() check of itself before doing unlock_new_inode(), so I would
expect unlock_new_inode() to indeed set the
file_system_type::i_mutex_dir_key.