scsi: target: core: Remove from tmr_list during LUN unlink

Currently TMF commands are removed from de_device.dev_tmf_list at the very
end of se_cmd lifecycle. However, se_lun unlinks from se_cmd upon a command
status (response) being queued in transport layer. This means that LUN and
backend device can be deleted in the meantime and a panic will occur:

target_tmr_work()
cmd->se_tfo->queue_tm_rsp(cmd); // send abort_rsp to a wire
transport_lun_remove_cmd(cmd) // unlink se_cmd from se_lun
- // - // - // -
<<<--- lun remove
<<<--- core backend device remove
- // - // - // -
qlt_handle_abts_completion()
tfo->free_mcmd()
transport_generic_free_cmd()
target_put_sess_cmd()
core_tmr_release_req() {
if (dev) { // backend device, can not be null
spin_lock_irqsave(&dev->se_tmr_lock, flags); //<<<--- CRASH

Call Trace:
NIP [c000000000e1683c] _raw_spin_lock_irqsave+0x2c/0xc0
LR [c00800000e433338] core_tmr_release_req+0x40/0xa0 [target_core_mod]
Call Trace:
(unreliable)
0x0
target_put_sess_cmd+0x2a0/0x370 [target_core_mod]
transport_generic_free_cmd+0x6c/0x1b0 [target_core_mod]
tcm_qla2xxx_complete_mcmd+0x28/0x50 [tcm_qla2xxx]
process_one_work+0x2c4/0x5c0
worker_thread+0x88/0x690

For the iSCSI protocol this is easily reproduced:

- Send some SCSI sommand

- Send Abort of that command over iSCSI

- Remove LUN on target

- Send next iSCSI command to acknowledge the Abort_Response

- Target panics

There is no need to keep the command in tmr_list until response completion,
so move the removal from tmr_list from the response completion to the
response queueing when the LUN is unlinked. Move the removal from state
list too as it is a subject to the same race condition.

Link: https://lore.kernel.org/r/[e-mail]
Fixes: c66ac9db8d4a ("[SCSI] target: Add LIO target core v4.0.0-rc6")
Reviewed-by: Roman Bolshakov <[e-mail]>
Reviewed-by: Mike Christie <[e-mail]>
Signed-off-by: Dmitry Bogdanov <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/target_core_tmr.c

···
 
 void core_tmr_release_req(struct se_tmr_req *tmr)
 {
-	struct se_device *dev = tmr->tmr_dev;
-	unsigned long flags;
-
-	if (dev) {
-		spin_lock_irqsave(&dev->se_tmr_lock, flags);
-		list_del_init(&tmr->tmr_list);
-		spin_unlock_irqrestore(&dev->se_tmr_lock, flags);
-	}
-
 	kfree(tmr);
 }
 
···
 			se_cmd->state_active = false;
 			spin_unlock_irqrestore(&dev->queues[i].lock, flags);
 
-			/*
-			 * Ensure that this ABORT request is visible to the LU
-			 * RESET code.
-			 */
-			if (!tmr->tmr_dev)
-				WARN_ON_ONCE(transport_lookup_tmr_lun(tmr->task_cmd) < 0);
-
 			if (dev->transport->tmr_notify)
 				dev->transport->tmr_notify(dev, TMR_ABORT_TASK,
 							   &aborted_list);
···
 		}
 
 		list_move_tail(&tmr_p->tmr_list, &drain_tmr_list);
+		tmr_p->tmr_dev = NULL;
 	}
 	spin_unlock_irqrestore(&dev->se_tmr_lock, flags);
 

drivers/target/target_core_transport.c

···
 	spin_unlock_irqrestore(&dev->queues[cmd->cpuid].lock, flags);
 }
 
+static void target_remove_from_tmr_list(struct se_cmd *cmd)
+{
+	struct se_device *dev = NULL;
+	unsigned long flags;
+
+	if (cmd->se_cmd_flags & SCF_SCSI_TMR_CDB)
+		dev = cmd->se_tmr_req->tmr_dev;
+
+	if (dev) {
+		spin_lock_irqsave(&dev->se_tmr_lock, flags);
+		if (cmd->se_tmr_req->tmr_dev)
+			list_del_init(&cmd->se_tmr_req->tmr_list);
+		spin_unlock_irqrestore(&dev->se_tmr_lock, flags);
+	}
+}
 /*
  * This function is called by the target core after the target core has
  * finished processing a SCSI command or SCSI TMF. Both the regular command
···
 static int transport_cmd_check_stop_to_fabric(struct se_cmd *cmd)
 {
 	unsigned long flags;
-
-	target_remove_from_state_list(cmd);
-
-	/*
-	 * Clear struct se_cmd->se_lun before the handoff to FE.
-	 */
-	cmd->se_lun = NULL;
 
 	spin_lock_irqsave(&cmd->t_state_lock, flags);
 	/*
···
 	if (!lun)
 		return;
 
+	target_remove_from_state_list(cmd);
+	target_remove_from_tmr_list(cmd);
+
 	if (cmpxchg(&cmd->lun_ref_active, true, false))
 		percpu_ref_put(&lun->lun_ref);
+
+	/*
+	 * Clear struct se_cmd->se_lun before the handoff to FE.
+	 */
+	cmd->se_lun = NULL;
 }
 
 static void target_complete_failure_work(struct work_struct *work)