ice: fix ice_remove_rule_internal vsi_list handling

When adding multiple VLANs to the same VSI, the ice_add_vlan code will
share the VSI list, so as not to create multiple unnecessary VSI lists.

Consider the following flow

  ice_add_vlan(hw, <VSI 0 VID 7, VSI 0 VID 8, VSI 0 VID 9>)

Where we add three VLAN filters for VIDs 7, 8, and 9, all for VSI 0.

The ice_add_vlan will create a single vsi_list and share it among all
the filters.

Later, if we try to remove a VLAN,

  ice_remove_vlan(hw, <VSI 0 VID 7>)

Then the removal code will update the vsi_list and remove VSI 0 from it.
But, since the vsi_list is shared, this breaks the list for the other
users who reference it. We actually even free the VSI list memory, and
may result in segmentation faults.

This is due to the way that VLAN rule share VSI lists with reference
counts, and is caused because we call ice_rem_update_vsi_list even when
the ref_cnt is greater than one.

To fix this, handle the case where ref_cnt is greater than one
separately. In this case, we need to remove the associated rule without
modifying the vsi_list, since it is currently being referenced by
another rule. Instead, we just need to decrement the VSI list ref_cnt.

The case for handling sharing of VSI lists with multiple VSIs is not
currently supported by this code. No such rules will be created today,
and this code will require changes if/when such code is added.
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ice/ice_switch.c

@@ -1538,9 +1538,20 @@ ice_remove_rule_internal(struct ice_hw *hw, u8 recp_id,
 	} else if (!list_elem->vsi_list_info) {
 		status = ICE_ERR_DOES_NOT_EXIST;
 		goto exit;
-	} else {
-		if (list_elem->vsi_list_info->ref_cnt > 1)
+	} else if (list_elem->vsi_list_info->ref_cnt > 1) {
+		/* a ref_cnt > 1 indicates that the vsi_list is being
+		 * shared by multiple rules. Decrement the ref_cnt and
+		 * remove this rule, but do not modify the list, as it
+		 * is in-use by other rules.
+		 */
 		list_elem->vsi_list_info->ref_cnt--;
+		remove_rule = true;
+	} else {
+		/* a ref_cnt of 1 indicates the vsi_list is only used
+		 * by one rule. However, the original removal request is only
+		 * for a single VSI. Update the vsi_list first, and only
+		 * remove the rule if there are no further VSIs in this list.
+		 */
 		vsi_handle = f_entry->fltr_info.vsi_handle;
 		status = ice_rem_update_vsi_list(hw, vsi_handle, list_elem);
 		if (status)