Re: [PATCH v2] NFSv4: fairly test all delegations on a SEQ4_ revocation

[Benjamin Coddington <bcodding@redhat.com>]

On 24 Aug 2023, at 14:52, Benjamin Coddington wrote:

> When the client is required to use TEST_STATEID to discover which
> delegation(s) have been revoked, it may continually test delegations at the
> head of the list if the server continues to be unsatisfied and send
> SEQ4_STATUS_RECALLABLE_STATE_REVOKED.  For a large number of delegations
> this behavior is prone to live-lock because the client may never be able to
> test and free revoked state at the end of the list since the
> SEQ4_STATUS_RECALLABLE_STATE_REVOKED will cause us to flag delegations at
> the head of the list to be tested.  This problem is further exacerbated by
> the state manager's willingness to be scheduled out on a busy system while
> testing the list of delegations.
>
> Keep a generation counter for each attempt to test all delegations, and
> skip delegations that have already been tested in the current pass.
>
> Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
> ---
>  fs/nfs/delegation.c       | 7 ++++++-
>  fs/nfs/delegation.h       | 1 +
>  include/linux/nfs_fs_sb.h | 1 +
>  3 files changed, 8 insertions(+), 1 deletion(-)
>
> --
>
> Changed on v2: remove extra brackets that had my debug statements

Hi potential reviewers - this can also be fixed with the simple addition of
a flag instead of a counter on every delegation, the only cost being that
nfs_server_reap_expired_delegations() would need to walk the whole list a
final time to remove the flag before returning.

The unsigned long counter is probably overkill.  Any thoughts?

Ben