Re: Just a small reminder

["William L. Jones" <jones@xxxxxxxxxxxxxxxxxx>]

At 12:11 PM 9/17/00 -0500, William L. Jones wrote:
> At 08:50 AM 9/17/00 -0500, lord@xxxxxxx wrote:
> > >
> > >
> > > The use the dentry d_iput function creates a problem with nfsd.   It to
> > > creates a dentry from an iget like open_by_filehndle and will cause
> > > vnode reference  problems.  Couldn't this problem be solved cleaner
> > > by using the linux provided iop functions like put_inode and clear_inode.
> > > Then the nfs would not have special case for xfs.
> > >
> > >
> > > Given the way the vn_rele works currently is their a problem with it
> > > marking the vnode inactive.   Linux will retain
> > > the inode in its cache until it decides to prune it, which means it may
> > > reuse it.   Wouldn't it be
> > > better to mark it inactive in a clear_inode call?
> > >
> > >
> > > Bill Jones
> >
> > Yes, I am aware of this. The issues here are that the put_inode method is
> > racey in that it always calls put inode, then does an atomic decrement and
> > lock on the count. Only if the count hits zero does it obtain a lock and do
> > special processing. It is quite possible we would call the inactive code,
> > and then have something else grab a reference count.
>
> But you have the same problem with the current code.  Their
> is no difference between using dcache d_iput or the supper operation 
> put_inode.!
> In both cases most of the iput work is done after the call to vn_rele.
> The second method is better since it works with nfsd.
>
> Can xfs_inactive sleep? It it can then both methods have a problem because
> it is possible to have a d_iput or iput running vn_rele at the same time
> and i_count will be greater then 1!

Oops! If we get to xfs_inactive it is the last iput.  I still
worry that it is possible for two iput to be done at the same time
give that the that vn_rele does a VN_LOCK.  If you are doing a lock
you can sleep!  Still this may only be a mpp thing!


Using d_iput is not perfect either as we cannot hold a lock across all of it.

> > Marking the vnode inactive is not a problem here, we do not remove the inode
> > from the system at this point, that is done in the clear inode phase. In
> > fact XFS will keep xfs inodes after the linux inode has gone in some cases.
> > We cannot use clear_inode to call inactive, as you only get here on inode
> > reuse. This is a long time later.
> I found the clear_inode code!
>
> > Steve