Hi Olga,
On Wed, Dec 3, 2014 at 2:54 PM, Olga Kornievskaia <aglo@xxxxxxxxx> wrote:
> Hi folks,
>
> I would like an opinion about changing code in such as way that we
> don't select a delegation stateid for an IO operation when this
> particular delegation is being returned.
>
> The reason it's some what problematic is that we send out a
> DELEG_RETURN and then we don't remove the stateid until we receive a
> reply. In the mean while, an IO operation can be happening and in
> nfs4_select_rw_stateid() it sees a delegation stateid and uses it.
> Well, at the server, it finishes processing DELEG_RETURN before
> getting an IO op and by that time the server is finished with the
> stateid and can error an IO operation with BAD_STATEID.
>
> diff --git a/fs/nfs/delegation.c b/fs/nfs/delegation.c
> index 7f3f606..4f6f6c9 100644
> --- a/fs/nfs/delegation.c
> +++ b/fs/nfs/delegation.c
> @@ -854,7 +854,8 @@ bool nfs4_copy_delegation_stateid(nfs4_stateid
> *dst, struct inode *in
> flags &= FMODE_READ|FMODE_WRITE;
> rcu_read_lock();
> delegation = rcu_dereference(nfsi->delegation);
> - ret = (delegation != NULL && (delegation->type & flags) == flags);
> + ret = (delegation != NULL && (delegation->type & flags) == flags &&
> + !test_bit(NFS_DELEGATION_RETURNING, &delegation->flags));
> if (ret) {
> nfs4_stateid_copy(dst, &delegation->stateid);
> nfs_mark_delegation_referenced(delegation);
The above cannot eliminate the possibility that we won't use a
delegation while it is being returned. It will at best just reduce the
window of opportunity.
So, why is this being considered to be a problem in the first place?
Are you seeing a measurable performance impact on a real life workload
(as opposed to some 1-in-a-billion occurrence from a QA test :-))?
Cheers
Trond
--
Trond Myklebust
Linux NFS client maintainer, PrimaryData
trond.myklebust@xxxxxxxxxxxxxxx
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