[PATCH net-next v4 8/9] ibmveth: wait for the RX poll to return before freeing the RX queue

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

napi_disable() returns once ibmveth_poll() has called
napi_complete_done(), but the poll is not finished: it then re-enables
the interrupt and calls ibmveth_rxq_pending_buffer(), which reads the
RX queue. ibmveth_close() can free that queue in the meantime, and the
late enable can leave the interrupt unmasked after close() masked it.
The request_irq() failure path in ibmveth_open() frees the same memory
after napi_disable() too.

Call synchronize_net() after napi_disable() on both paths. Every
caller of ibmveth_poll() runs it with bottom halves or interrupts
disabled, so this waits for the poll to return.

Found by AI-assisted review of the ibmveth multi-queue RX series and
confirmed by code inspection; also raised by the Sashiko AI review of
the first version of this series. The race was not reproduced. Tested
on a POWER10 LPAR under an incoming ping flood with 30 rapid link
down/up cycles and 30 rapid MTU cycles (1500 <-> 9000); ran cleanly
with no warnings or faults. No kernel selftests cover ibmveth.

Fixes: bea3348eef27 ("[NET]: Make NAPI polling independent of struct net_device objects.")
Signed-off-by: Mingming Cao <mmc@linux.ibm.com>
---
Changes in v2:
- new patch; raised by the Sashiko review of v1 patch 1 as a
  pre-existing bug

 drivers/net/ethernet/ibm/ibmveth.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index f2570d637301..85e176d0ed32 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c
@@ -768,6 +768,7 @@ static int ibmveth_open(struct net_device *netdev)
 			 netdev);
 	if (rc != 0) {
 		napi_disable(&adapter->napi);
+		synchronize_net();
 		netdev_err(netdev, "unable to request irq 0x%x, rc %d\n",
 			   netdev->irq, rc);
 		goto out_free_buffer_pools;
@@ -834,6 +835,11 @@ static int ibmveth_close(struct net_device *netdev)
 	netdev_dbg(netdev, "close starting\n");
 
 	napi_disable(&adapter->napi);
+	/* napi_disable() returns once ibmveth_poll() has called
+	 * napi_complete_done(), but the poll still re-enables the
+	 * interrupt and reads the RX queue after that.
+	 */
+	synchronize_net();
 
 	netif_tx_disable(netdev);
 
-- 
2.50.1 (Apple Git-155)