On Mon, 2017-06-05 at 15:57 +0000, Bart Van Assche wrote:
> On Sat, 2017-06-03 at 22:10 +0000, Nicholas A. Bellinger wrote:
> > +static bool target_lookup_lun_from_tag(struct se_session *se_sess, u64 tag,
> > + u64 *unpacked_lun)
> > +{
> > + struct se_cmd *se_cmd;
> > + unsigned long flags;
> > + bool ret = false;
> > +
> > + spin_lock_irqsave(&se_sess->sess_cmd_lock, flags);
> > + list_for_each_entry(se_cmd, &se_sess->sess_cmd_list, se_cmd_list) {
> > + if (se_cmd->se_cmd_flags & SCF_SCSI_TMR_CDB)
> > + continue;
> > +
> > + if (se_cmd->tag == tag) {
> > + *unpacked_lun = se_cmd->orig_fe_lun;
> > + ret = true;
> > + break;
> > + }
> > + }
> > + spin_unlock_irqrestore(&se_sess->sess_cmd_lock, flags);
> > +
> > + return ret;
> > +}
> > +
> > /**
> > * target_submit_tmr - lookup unpacked lun and submit uninitialized se_cmd
> > * for TMR CDBs
> > @@ -1639,19 +1662,31 @@ int target_submit_tmr(struct se_cmd *se_cmd, struct se_session *se_sess,
> > core_tmr_release_req(se_cmd->se_tmr_req);
> > return ret;
> > }
> > + /*
> > + * If this is ABORT_TASK with no explicit fabric provided LUN,
> > + * go ahead and search active session tags for a match to figure
> > + * out unpacked_lun for the original se_cmd.
> > + */
> > + if (tm_type == TMR_ABORT_TASK && (flags & TARGET_SCF_LOOKUP_LUN_FROM_TAG)) {
> > + if (!target_lookup_lun_from_tag(se_sess, tag, &unpacked_lun))
> > + goto failure;
> > + }
> >
> > ret = transport_lookup_tmr_lun(se_cmd, unpacked_lun);
> > - if (ret) {
> > - /*
> > - * For callback during failure handling, push this work off
> > - * to process context with TMR_LUN_DOES_NOT_EXIST status.
> > - */
> > - INIT_WORK(&se_cmd->work, target_complete_tmr_failure);
> > - schedule_work(&se_cmd->work);
> > - return 0;
> > - }
> > + if (ret)
> > + goto failure;
> > +
> > transport_generic_handle_tmr(se_cmd);
> > return 0;
>
> Hello Nic,
>
> So after LUN lookup has finished sess_cmd_lock lock is dropped, a context
> switch occurs due to the queue_work() call in transport_generic_handle_tmr()
> and next core_tmr_abort_task() reacquires that lock? Sorry but I'm afraid
> that if after that lock is dropped and before it is reacquired a command
> finishes and the initiator reuses the same tag for another command for the
> same LUN that this may result in the wrong command being aborted.
This is only getting a unpacked_lun to determine where the incoming
ABORT_TASK should perform a se_lun lookup and percpu ref upon.
The scenario you are talking about would require a tag be reused on the
same session for the same device between when the ABORT_TASK is
dispatched here, and actually processed.
Because qla2xxx doesn't reuse tags, it's not a problem since it's the
only consumer of TARGET_SCF_LOOKUP_LUN_FROM_TAG.
Since Himanshu and Quinn are OK it with, I'm OK with it.
If you have another driver that needs to use this logic where an
ABORT_TASK doesn't know the unpacked_lun to reference, and does reuse
tags then I'd consider a patch for that.
