[PATCH net-next v3 6/8] ibmveth: return the error when set_channels cannot add TX queues

[Mingming Cao <mmc@linux.ibm.com>]

When ibmveth_set_channels() cannot allocate a TX buffer for a new
queue, it falls back to the old queue count, and the successful
netif_set_real_num_tx_queues() call then overwrites rc. ethtool -L
reports success while the queue count is unchanged.

Return the allocation error when the fallback succeeds.

Found by AI-assisted review of the ibmveth multi-queue RX series and
confirmed by code inspection. Tested on a POWER10 LPAR with the TX
buffer allocation forced to fail by a test-only module parameter (not
part of this patch): ethtool -L tx 8 now fails with -ENOMEM and the
device keeps its four queues and passes traffic. No kernel selftests
cover ibmveth.

Fixes: 10c2aba89cc0 ("ibmveth: Ethtool set queue support")
Signed-off-by: Mingming Cao <mmc@linux.ibm.com>
---
 drivers/net/ethernet/ibm/ibmveth.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index dc5e63b7369e..18eb0f27512e 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c
@@ -1178,7 +1178,7 @@ static int ibmveth_set_channels(struct net_device *netdev,
 	struct ibmveth_adapter *adapter = netdev_priv(netdev);
 	unsigned int old = netdev->real_num_tx_queues,
 		     goal = channels->tx_count;
-	int rc, i;
+	int rc, i, alloc_rc = 0;
 
 	/* If the device is not open (including a failed close/open with
 	 * IFF_UP still set) then don't allocate, just set desired
@@ -1204,6 +1204,7 @@ static int ibmveth_set_channels(struct net_device *netdev,
 		/* if something goes wrong, free everything we just allocated */
 		netdev_err(netdev, "Failed to allocate more tx queues, returning to %d queues\n",
 			   old);
+		alloc_rc = rc;
 		goal = old;
 		old = i;
 		break;
@@ -1214,6 +1215,8 @@ static int ibmveth_set_channels(struct net_device *netdev,
 			   old);
 		goal = old;
 		old = i;
+	} else if (alloc_rc) {
+		rc = alloc_rc;
 	}
 	/* Free any that are no longer needed */
 	for (i = old; i > goal; i--) {
-- 
2.50.1 (Apple Git-155)