Re: [PATCH net-next v5 04/15] ibmveth: Refactor buffer pool management for per-queue MQ RX

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ibmveth: Refactor buffer pool management for per-queue MQ RX

This moves the five RX buffer pools to a per-queue array and introduces
ibmveth_alloc_buffer_pools() / ibmveth_free_buffer_pools() plus the
per-queue helpers, wiring them into open() and close(). Queue 0 stays the
template for pool geometry and activation, and runtime is still
single-queue.

A few questions below about the new unwind paths and about two of the
new comments.

[ ... ]

+/**
+ * ibmveth_alloc_queue_buffer_pools - Allocate buffer pools for a single queue
+ * @adapter: ibmveth adapter structure
+ * @queue: queue index
+ *
+ * Allocates backing storage for each active pool on @queue.
+ * Inactive pools (!active) are skipped. Pool metadata must be
+ * initialized before calling this function.
+ *
+ * Return: 0 on success, negative error code on failure
+ */
+static int ibmveth_alloc_queue_buffer_pools(struct ibmveth_adapter *adapter,
+					    int queue)
+{
+	struct net_device *netdev = adapter->netdev;
+	int i;
+
+	for (i = 0; i < IBMVETH_NUM_BUFF_POOLS; i++) {
+		struct ibmveth_buff_pool *bpool =
+			&adapter->rx_buff_pool[queue][i];
+
+		if (!bpool->active)
+			continue;
+
+		if (ibmveth_alloc_buffer_pool(bpool)) {
+			netdev_err(netdev,
+				   "queue %d pool %d alloc failed (size=%u count=%u)\n",
+				   queue, i,
+				   bpool->buff_size,
+				   bpool->size);
+			bpool->active = 0;
+			/* Free by allocation presence, not active — the
+			 * failing pool cleared active first and would be
+			 * skipped by an active-only unwind.
+			 */

[Severity: Low]
Is the stated rationale in this comment accurate?  Freeing by allocation
presence is a fine policy for the later resize paths, but the specific
claim that an active-only unwind would skip the failing pool and leak it
does not seem to hold here, because ibmveth_alloc_buffer_pool() already
undoes its own partial allocations before returning -1:

drivers/net/ethernet/ibm/ibmveth.c:ibmveth_alloc_buffer_pool() {
	pool->dma_addr = kzalloc_objs(dma_addr_t, pool->size);
	if (!pool->dma_addr) {
		kfree(pool->free_map);
		pool->free_map = NULL;
		return -1;
	}

	pool->skbuff = kcalloc(pool->size, sizeof(void *), GFP_KERNEL);

	if (!pool->skbuff) {
		kfree(pool->dma_addr);
		pool->dma_addr = NULL;

		kfree(pool->free_map);
		pool->free_map = NULL;
		return -1;
	}
	...
}

By the time bpool->active = 0 runs, free_map/dma_addr/skbuff are all NULL
for the failing pool, so there is nothing for an active-only unwind to
miss.  The same claim appears in the changelog ("v4 fail path freed by
active and skipped the failing pool", "open-fail cannot leak partially
allocated pools").  Could the comment and changelog instead justify
free-by-presence purely in terms of the later resize paths?

+			ibmveth_free_queue_buffer_pools(adapter, queue);
+			return -ENOMEM;
+		}
+	}
+
+	return 0;
+}
+

[ ... ]

+	/* Allocate actual buffers for all queues */
+	for (q = 0; q < adapter->num_rx_queues; q++) {
+		rc = ibmveth_alloc_queue_buffer_pools(adapter, q);
+		if (rc) {
+			/* Free pools for all previous queues */
+			while (--q >= 0)
+				ibmveth_free_queue_buffer_pools(adapter, q);
+			return rc;
+		}
+	}
+
+	netdev_dbg(netdev, "allocated buffer pools for %d queue(s)\n",
+		   adapter->num_rx_queues);

[Severity: Low]
This isn't a bug, but adapter->num_rx_queues is declared as
"unsigned int num_rx_queues;" in drivers/net/ethernet/ibm/ibmveth.h, so
should these two new messages use %u rather than %d?  The same applies to
the netdev_dbg() in ibmveth_free_buffer_pools() below.

[Severity: Medium]
This isn't a gap introduced by this patch (the old inline pool loop fell
through to the same labels), but since the edge is being rewritten here:
this goto is taken after ibmveth_register_logical_lan() has already
succeeded, and the unwind it lands on never issues h_free_logical_lan():

out_free_tx_ltb:
	while (--i >= 0)
		ibmveth_free_tx_ltb(adapter, i);
	ibmveth_cleanup_rx_resources(adapter);
out_free_filter_list:
	ibmveth_free_filter_list(adapter);

ibmveth_cleanup_rx_resources() does the dma_unmap_single() of
buffer_list_dma[], the dma_free_coherent() of the RX completion queue and
the free_page() of the buffer-list page, and ibmveth_free_filter_list()
releases the filter list, all while PHYP still holds those addresses.  The
adjacent request_irq() failure path does perform the handshake the driver
otherwise considers mandatory:

		do {
			lpar_rc = h_free_logical_lan(adapter->vdev->unit_address);
		} while (H_IS_LONG_BUSY(lpar_rc) || (lpar_rc == H_BUSY));

Can PHYP write the rx_no_buffer counter into the freed buffer-list page, or
post a completion into the freed RX queue, after this path returns?  The
h_vio_signal(VIO_IRQ_DISABLE) issued just before registration also is not
rebalanced here.

Later patches in this series do repair this: "ibmveth: Refactor TX resource
allocation in open/close paths" retargets this edge to out_unregister_lan,
and by the end of the series ibmveth_open() allocates the pools before
ibmveth_register_rx_queues() and routes post-registration failures through
ibmveth_free_all_queues() -> h_free_logical_lan().  Would it be reasonable
to point this goto at a label that unregisters the logical LAN already in
this patch, so the intermediate commit is not bisect-visible?

[Severity: Medium]
This is a pre-existing issue rather than one introduced here, but does this
hunk silently fix a TX long-term-buffer leak?

In the parent commit the pool unwind consumed i:

out_free_buffer_pools:
	while (--i >= 0) {
		if (adapter->rx_buff_pool[0][i].active)
			ibmveth_free_buffer_pool(adapter,
						 &adapter->rx_buff_pool[0][i]);
	}
out_free_tx_ltb:
	while (--i >= 0)
		ibmveth_free_tx_ltb(adapter, i);

so on reaching out_free_tx_ltb by fall-through, i was already -1 and the
first test of --i evaluated to -2, meaning no tx_ltb_ptr[]/tx_ltb_dma[]
buffer was released.  With the pool unwind now a helper call that does not
touch i, i still holds the TX queue count from the completed TX allocation
loop, so the TX LTBs are freed.

Every PAGE_ALIGN(IBMVETH_MAX_TX_BUF_SIZE) TX buffer plus its DMA mapping was
leaked on each failing open, and it repeats per attempt ("ip link set <dev>
up" under memory pressure, or the close+open pair inside veth_pool_store(),
ibmveth_change_mtu() and ibmveth_reset()).

Would it make sense to split this out as its own patch with a Fixes: tag so
stable trees pick it up, or at least describe it in the changelog?

[ ... ]