Re: [PATCH] qla_target: Check refcount in find_sess_by_*

[Roland Dreier <roland@xxxxxxxxxxxxxxx>]

> Mmmmm, I'd still like to try to avoid (another) atomic op in the fast
> path w/ hardware_lock held if at all possible..

atomic_read() is not an atomic op.

However this patch is not right, see below.

> Also thinking more about the case in your comment, I'm starting to
> wonder if tcm_qla2xxx_free_session() should be obtaining hardware_lock +
> clearing the s_id and loop_id lookup entries earlier than currently
> done..
>
> That is, target_wait_for_sess_cmds() is called before clearing the
> nodeacl pointers from s_id + loop_id in tcm_qla2xxx_free_session(),
> which means that we still perform se_node_acl lookups in the case where
> the individual tcm_qla2xxx endpoint was not also being shutdown as
> well..
>
> So that said, I think your work-around is OK to address the current BUG,
> but the s_id + loop_id clearing order in tcm_qla2xxx_free_session()
> would be having an effect here as well..

Yes, in fact we need to clear the session from all lookup tables
even earlier than ->free_session.  We need to make sure that as
soon as target_release_session() is called, that session will no
longer be used for any new commands.

So qla_tgt_unreg_sess() needs to clear the session from the
"by loop_id" table as well as the "by fc_id" table.

 - R.
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