Re: [PATCH net-next v4 14/14] ibmveth: Fix MQ RX poll and shutdown hangs after queue resize

On 8/6/26 11:37 AM, Jakub Kicinski wrote:

This is an AI-generated review of your patch. The human sending this
email has considered the AI review valid, or at least plausible.
---
ibmveth: Fix MQ RX poll and shutdown hangs after queue resize

This changes ibmveth_poll() to skip RX slots whose correlator cannot be
mapped to a buffer pool instead of retrying them forever, completes NAPI
when the interface is going down, and adds a descriptor length check
before skb_put().  The WARN_ON plus adapter reset escalation in the
correlator validation paths is replaced by a rate-limited message.

No Link: tags present in the commit header.

A few questions below.

Hi Jakub,

Thanks for the review and follow-up.

[Severity: Low]
Would it make sense to split this into separate patches with individual
Fixes: tags?  There appear to be four independent changes here:

   - skipping bad RX correlators and dropping the WARN_ON/reset escalation
   - completing NAPI when the interface is down or napi_disable is pending
   - validating the descriptor length against skb tailroom before skb_put()
   - changing the return value on the budget-exhausted shutdown path

There is no Fixes: tag, so stable maintainers cannot pick up the hang fix
without also picking up the policy change that removes the reset based
recovery, and the skb_put() hardening is not visible as a fix on its own.

I’ll fold these back into the introducing patches rather than keep a
mixed trailer or invent broad `Fixes:` tags.

These are MQ-series issues in the new poll/resize/teardown paths, not

fixes for older pre-MQ behavior, so I do not think they should be
presented as separate `net` backports.

The better restack is to fold each piece into the patch that introduces
the behavior:
- P05: mask IRQ when napi_schedule_prep() fails
- P09: stopping guards, wrap-safe length validation, honest harvest
- P12: teardown-first resize fix, correlator liveness, residual
   skip+schedule_work handling

So I’ll restack this into the owning patches for v5; P14 may
disappear entirely if nothing independent remains after the fold-back,
rather than keeping one mixed patch with broad `Fixes:` tags.

quoted

diff --git a/drivers/net/ethernet/ibm/ibmveth.c b/drivers/net/ethernet/ibm/ibmveth.c
index c99d8e8be7b37..09e06d86701a5 100644
--- a/drivers/net/ethernet/ibm/ibmveth.c
+++ b/drivers/net/ethernet/ibm/ibmveth.c

@@ -1376,6 +1376,24 @@ ibmveth_free_single_rx_queue(struct ibmveth_adapter *adapter, int queue_idx)
  	netdev_dbg(adapter->netdev, "Freed queue %d resources\n", queue_idx);
  }
  
+static bool ibmveth_rxq_correlator_valid(struct ibmveth_adapter *adapter,
+					 int queue_index, u64 correlator)
+{
+	unsigned int pool = correlator >> 32;
+	unsigned int index = correlator & 0xffffffffUL;
+
+	return pool < IBMVETH_NUM_BUFF_POOLS &&
+	       index < adapter->rx_buff_pool[queue_index][pool].size;
+}

[Severity: High]
This isn't a bug introduced by this patch, since the pre-existing WARN_ON
checks were also bounds-only, but can a correlator naming an inactive or
already freed pool still pass ibmveth_rxq_correlator_valid() and then
dereference a NULL array?

ibmveth_init_buffer_pool() sets pool->size for all pools regardless of
active state, while ibmveth_alloc_queue_buffer_pools() skips inactive
pools, and ibmveth_free_buffer_pool() clears the arrays without clearing
size or active:

	kfree(pool->free_map);
	pool->free_map = NULL;
	...
	if (pool->skbuff) {
		kfree(pool->skbuff);
		pool->skbuff = NULL;
	}

With the defaults in ibmveth.h:

	static int pool_count[] = { 256, 512, 256, 256, 256 };
	static int pool_active[] = { 1, 1, 0, 0, 0};

a correlator of pool=2, index=0 satisfies both conditions of the new
helper, and both users then index a NULL pointer before the !skb test can
help:

	return adapter->rx_buff_pool[queue_index][pool].skbuff[index];

and

	skb = adapter->rx_buff_pool[queue_index][pool].skbuff[index];

Should the helper also require pool->active and non-NULL skbuff/dma_addr/
free_map, or should ibmveth_free_buffer_pool() clear pool->size?  The same
window seems to apply to pools torn down by ethtool -L scale-down, an MTU
change, or sysfs deactivation.

Yes. Bounds-only validation is too weak here.

I’ll make the helper require an active pool plus non-NULL
skbuff/free_map state, and clear the freed pool state so it no longer
looks in-range after teardown. That belongs with the resize teardown
story, because the real bug is freeing pool state while stale
correlators can still arrive.

[Severity: Low]
This is a pre-existing weakness rather than something new here, but the
helper only bounds-checks, so a stale correlator that happens to land in
range after an ethtool -L resize is treated as a live frame.  With
reuse=false the buffer can be handed to the stack while the hypervisor may
still own it, and with reuse=true the index is pushed onto free_map a
second time.  Is there any generation counter or per-queue tag available in
the correlator that could distinguish a stale descriptor from a current
one?

No, there is no generation field in the correlator today.

I don’t plan to add one in this series. I think the right fix here is
to close the ownership/teardown hole in P12 so PHYP is no longer
posting into pool state we already tore down. With that fixed, the
stronger liveness checks should be enough as belt-and-braces, without
adding a larger generation/tag change in this cycle.

quoted

+
+static void ibmveth_rxq_advance(struct ibmveth_rx_q *rxq)
+{
+	if (++rxq->index == rxq->num_slots) {
+		rxq->index = 0;
+		rxq->toggle = !rxq->toggle;
+	}
+}
+
  /**
   * ibmveth_remove_buffer_from_pool - remove a buffer from a pool
   * @adapter: adapter instance

@@ -1397,17 +1415,12 @@ static int ibmveth_remove_buffer_from_pool(struct ibmveth_adapter *adapter,
  	unsigned int free_index;
  	struct sk_buff *skb;
  
-	if (WARN_ON(pool >= IBMVETH_NUM_BUFF_POOLS) ||
-	    WARN_ON(index >= adapter->rx_buff_pool[queue_index][pool].size)) {
-		schedule_work(&adapter->work);
+	if (!ibmveth_rxq_correlator_valid(adapter, queue_index, correlator))
  		return -EINVAL;
-	}
  
  	skb = adapter->rx_buff_pool[queue_index][pool].skbuff[index];
-	if (WARN_ON(!skb)) {
-		schedule_work(&adapter->work);
+	if (!skb)
  		return -EFAULT;
-	}

[Severity: Medium]
The schedule_work(&adapter->work) escalation is dropped here and in
ibmveth_rxq_get_buffer(), so nothing bounds the condition any more.  The
commit message describes the new skip policy but does not mention that all
recovery escalation is gone.

The previous reset performed a close/open cycle, which issued
h_free_logical_lan and re-registered the logical LAN, flushing every buffer
registration the hypervisor still held.  If the bad correlator exists
because PHYP still holds buffers from a pool that
ibmveth_free_buffer_pool() already unmapped and freed during an
ethtool -L resize:

	dma_unmap_single(&adapter->vdev->dev, pool->dma_addr[i],
			 pool->buff_size, DMA_FROM_DEVICE);
	dev_kfree_skb_any(skb);

can the hypervisor keep writing into those freed pages indefinitely now
that the driver only logs and advances?

Separately, this also folds together two different classes: -EINVAL for an
out-of-range correlator, and -EFAULT where pool and index are in range but
skbuff[index] is NULL, which indicates driver/hypervisor state desync.  Is
silently skipping the -EFAULT case intended?

And if the descriptor's correlator belongs to a different queue's pool, the
skip never reclaims that queue's slot, so that pool's available count stays
inflated and ibmveth_replenish_task() stops replenishing it:

	if (pool->active && pool->free_map &&
	    (atomic_read(&pool->available) < pool->threshold))

Agreed — skip-only was not sufficient on its own.

The real fix belongs in P12, in the earlier resize/teardown path:
drain, deregister with h_free_logical_lan_queue(), then unmap/free, so
PHYP ownership is released before the pool memory goes away. After
that, I’ll keep residual bad-slot handling with rate-limited logging
plus schedule_work() as secondary recovery, rather than treating
skip-and-advance as the primary answer.

quoted

  
  	/* if we are going to reuse the buffer then keep the pointers around
  	 * but mark index as available. replenish will see the skb pointer and

@@ -1452,11 +1465,8 @@ ibmveth_rxq_get_buffer(struct ibmveth_adapter *adapter,
  	unsigned int pool = correlator >> 32;
  	unsigned int index = correlator & 0xffffffffUL;
  
-	if (WARN_ON(pool >= IBMVETH_NUM_BUFF_POOLS) ||
-	    WARN_ON(index >= adapter->rx_buff_pool[queue_index][pool].size)) {
-		schedule_work(&adapter->work);
+	if (!ibmveth_rxq_correlator_valid(adapter, queue_index, correlator))
  		return NULL;
-	}
  
  	return adapter->rx_buff_pool[queue_index][pool].skbuff[index];
  }

@@ -1483,14 +1493,15 @@ static int ibmveth_rxq_harvest_buffer(struct ibmveth_adapter *adapter,
  
  	cor = rxq->queue_addr[rxq->index].correlator;
  	rc = ibmveth_remove_buffer_from_pool(adapter, cor, queue_index, reuse);
-	if (unlikely(rc))
+	if (unlikely(rc)) {
+		if (rc == -EINVAL || rc == -EFAULT)
+			goto advance;
  		return rc;
-
-	if (++rxq->index == rxq->num_slots) {
-		rxq->index = 0;
-		rxq->toggle = !rxq->toggle;
  	}
  
+advance:
+	ibmveth_rxq_advance(rxq);
+
  	return 0;
  }

[Severity: Low]
Can ibmveth_rxq_harvest_buffer() still return non-zero after this change?
ibmveth_remove_buffer_from_pool() has exactly three returns: -EINVAL,
-EFAULT and 0, and both error codes now go to the advance label, so
"return rc;" looks unreachable.

That would make all five "if (unlikely(rc)) break;" checks in
ibmveth_poll(), including the two added by this patch, dead code, along
with the harvest failure path in ibmveth_drain_rx_queue():

	rc = ibmveth_rxq_harvest_buffer(adapter, queue_index, true);
	if (rc) {
		netdev_err(netdev,
			   "Failed to harvest buffer from queue %d during drain: %d\n",
			   queue_index, rc);
		break;
	}
	drained++;

Should unmappable slots encountered during drain still be counted as
drained++ with no diagnostic?  The kernel-doc above harvest still documents
"other - non-zero return from ibmveth_remove_buffer_from_pool", which no
longer matches the implementation.

As mailed, not for -EINVAL/-EFAULT, so that part was misleading.

I’ll make harvest advance and return rc for -EINVAL/-EFAULT, with
poll/drain continuing past those slots without treating them as
successful receives. I’ll fold that into the earlier poll logic patch
rather than leaving it here as a trailer cleanup.

quoted

@@ -3092,11 +3103,19 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
  	if (WARN_ON(queue_index < 0 || queue_index >= adapter->num_rx_queues))
  		return 0;
  
+	if (!netif_running(netdev) || napi_disable_pending(napi)) {
+		napi_complete_done(napi, 0);
+		return 0;
+	}
+
  	if (adapter->rx_qstats)
  		adapter->rx_qstats[queue_index].polls++;
  
  restart_poll:
  	while (frames_processed < budget) {
+		if (!netif_running(netdev) || napi_disable_pending(napi))
+			break;
+
  		if (!ibmveth_rxq_pending_buffer(adapter, queue_index))
  			break;
  

[ ... ]

quoted

@@ -3126,8 +3145,45 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
  			__sum16 iph_check = 0;
  
  			skb = ibmveth_rxq_get_buffer(adapter, queue_index);
-			if (unlikely(!skb))
-				break;
+			if (unlikely(!skb)) {
+				if (net_ratelimit())
+					netdev_err(netdev,
+						   "bad correlator on queue %d, skipping slot\n",
+						   queue_index);

[ ... ]

quoted

+
+			if (unlikely((unsigned int)offset +
+				     (unsigned int)length >
+				     skb_tailroom(skb))) {

[Severity: High]
This is not a regression from this patch, since there was no length check
at all before, but can this check be bypassed by 32-bit wraparound?

Both operands are cast to unsigned int, so the sum is modulo 2^32.  Unlike
offset, length is not masked; ibmveth_rxq_frame_length() returns the whole
descriptor field:

	return be32_to_cpu(rxq->queue_addr[rxq->index].length);

and in ibmveth.h that field is a full __be32 written by the hypervisor,
while only offset gets IBMVETH_RXQ_OFF_MASK (0x0000FFFF).

For a corrupted length like 0xFFFFFFF0 with a small offset, the addition
wraps to a small value and the guard does not fire.  The copybreak test
compares against "static unsigned int rx_copybreak", so 0xFFFFFFF0 is not
less than rx_copybreak and no copy skb is allocated, and execution reaches:

	skb_put(skb, length);

which trips skb_over_panic() -> BUG().  Would an overflow-safe form work
better here, for example:

	if (offset > tailroom || length > tailroom - offset)

or validating length against pool->buff_size?

[ ... ]

Yes. The sum-based check can wrap and still let skb_put() overrun.

I’ll switch that to the overflow-safe form, i.e. reject if offset is
already past tailroom or length exceeds the remaining room. That should
live with the patch that introduces the MQ poll path, not as a separate
end-of-series hardening patch.

quoted

@@ -3206,8 +3262,14 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
  
  	ibmveth_replenish_task(adapter, queue_index);
  
-	if (frames_processed == budget)
+	if (frames_processed == budget) {
+		if (!netif_running(netdev) || napi_disable_pending(napi)) {
+			napi_complete_done(napi, frames_processed);
+			/* After complete_done, must not return full budget. */
+			return frames_processed ? frames_processed - 1 : 0;
+		}
  		goto out;
+	}
  
  	if (!napi_complete_done(napi, frames_processed))
  		goto out;

@@ -3225,6 +3287,8 @@ static int ibmveth_poll(struct napi_struct *napi, int budget)
  	}
  
  	if (ibmveth_rxq_pending_buffer(adapter, queue_index) &&
+	    netif_running(netdev) &&
+	    !napi_disable_pending(napi) &&
  	    napi_schedule(napi)) {
  		lpar_rc = ibmveth_disable_irq(adapter, queue_index);
  		WARN_ON(lpar_rc != H_SUCCESS);

[Severity: High]
This isn't a bug introduced by this patch, as the
napi_complete_done() -> ibmveth_enable_irq() -> ibmveth_rxq_pending_buffer()
sequence is unchanged, but do the new guards actually close the shutdown
window the commit message describes?

The new mid-loop break also lands here with frames_processed < budget, so
the quiesce case still reaches:

	if (!napi_complete_done(napi, frames_processed))
		goto out;

Clearing NAPI_STATE_SCHED there is what napi_disable() waits for, so
ibmveth_close() can proceed past ibmveth_cleanup_rx_interrupts() into
ibmveth_cleanup_rx_resources():

	if (adapter->rx_queue[i].queue_addr) {
		dma_free_coherent(dev, adapter->rx_queue[i].queue_len,
				  adapter->rx_queue[i].queue_addr,
				  adapter->rx_queue[i].queue_dma);
		adapter->rx_queue[i].queue_addr = NULL;

while the still running poll executes:

	lpar_rc = ibmveth_enable_irq(adapter, queue_index);

re-arming the PHYP interrupt that close just masked, and then evaluates
ibmveth_rxq_pending_buffer(), which reads
rxq->queue_addr[rxq->index].flags_off - a NULL dereference or a read of
freed coherent memory.  ibmveth_close() has no synchronize_net() between
napi_disable()/free_irq() and the frees, unlike the scale-down path.

Note the new netif_running()/napi_disable_pending() terms are evaluated
after ibmveth_rxq_pending_buffer() in the same condition, so they cannot
prevent that access; they only suppress the following
ibmveth_disable_irq().

Related question on that suppression: in the window where
__LINK_STATE_START is already cleared by __dev_close_many() but
NAPI_STATE_DISABLE is not yet set, the pre-patch code re-masked PHYP via
the napi_schedule() branch.  With the new guards, poll now returns leaving
delivery unmasked into the napi_disable()/free_irq() window, and the
interrupt handler does not mask either when napi_schedule_prep() fails:

	if (napi_schedule_prep(napi)) {
		lpar_rc = ibmveth_disable_irq(adapter, qindex);
		WARN_ON(lpar_rc != H_SUCCESS);
		__napi_schedule(napi);
	}

Can that leave the queue interrupt storming until free_irq()?

[ ... ]

Yes, the mailed guards were incomplete.

The stopping path needs to complete without re-enabling IRQs once close
or napi_disable is in progress.

The schedule_rx_queue() path also still needs to mask the interrupt
when napi_schedule_prep() fails, so the queue does not stay unmasked
into the free_irq() window.

I’ll also keep synchronize_net() in close after RX IRQ/NAPI teardown
and before freeing queue resources, so any poll instance that already
passed the stopping checks is drained before the frees.

Thanks

Mingming