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From:   "Benjamin Coddington" <bcodding@redhat.com>
To:     "Trond Myklebust" <trondmy@hammerspace.com>
Cc:     linux-nfs@vger.kernel.org
Subject: Re: client lookup_revalidate bug
Date:   Thu, 30 May 2019 06:35:06 -0400
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On 29 May 2019, at 13:19, Trond Myklebust wrote:
> On Wed, 2019-05-29 at 12:39 -0400, Benjamin Coddington wrote:
>> On 29 May 2019, at 12:21, Trond Myklebust wrote:
>
> Sorry, but that's not the case, because of the abuse of the
> nosharecache flag. You are manipulating the file on the server and
> expecting an immediate cache invalidation. That would require
> information that the client does not have.

Yes, forget about the nosharecache flag.  Let's just assume we move the file
on the server.  The client does perform a GETATTR and sees the updated
change_attr for the directory, but it matches the dentry's new d_time.

I don't expect immediate cache invalidation; invalidation will never happen
as long as B/'s change_attr isn't bumped again.  On the client, B/foo
dentry's d_time is the same as the change_attr for B/, and even though
there's no file at B/foo on the server, the client will keep the B/foo
dentry until something else bumps B/'s change_attr.

Maybe I need to imagine a scenario where this matters more..

But, I think that if we use the method of comparing d_time with the parent's
change_attr to determine if we need to lookup, this is a case where that's
not reliable.

I'll try to come up with something as I have time to work on it since I am
getting pressure about it.  It looks to me like this behavior has been
around for a long time.  Thanks for the look.

Ben