Re: [PATCH] NFS: Revalidate once when holding a delegation

[Trond Myklebust <trondmy@hammerspace.com>]

On Fri, 2020-01-24 at 20:33 -0500, Benjamin Coddington wrote:
> On 24 Jan 2020, at 14:24, Trond Myklebust wrote:
> 
> > On Fri, 2020-01-24 at 09:09 -0500, Benjamin Coddington wrote:
> > 
> > This patch needs to fix nfs_force_lookup_revalidate() to avoid the
> > value NFS_DELEGATION_VERF.
> 
> I don't understand why.  Doesn't nfs_force_lookup_revalidate() just
> bump the
> directory's cache_change_attribute, which is value we don't care
> about at
> all here.  This patch just sets a magic value on the dentry's d_time
> after a
> revalidation occurs for that dentry while holding a delegation.  It
> doesn't
> care at all about the directory's change_attr.
> 
> What am I missing?

Those calls to nfs_set_verifier(dentry, nfs_save_change_attribute(dir))
are storing the parent directory cache_change_attribute() in the d_time
field of the child dentry. That's the normal value for the child dentry
verifiers of that directory when there is no delegation.

So to avoid collisions, you need to ensure that dir-
>cache_change_attribute never takes the value NFS_DELEGATION_VERF.


-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com