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

[mingming cao <mmc@linux.ibm.com>]

On 8/6/26 11:49 AM, Jakub Kicinski wrote:
> On Thu, 30 Jul 2026 17:47:17 -0700 Mingming Cao wrote:
>> After aggressive ethtool -L cycling, PHYP can leave a VALID RX descriptor
>> with a correlator that no longer matches the per-queue buffer pools. Poll
>> treated this as fatal: ibmveth_rxq_get_buffer() WARNed and returned NULL
>> without advancing the ring, then restart_poll retried the same slot
>> forever.
>>
>> Advance past bad correlators instead of spinning: validate correlators
>> without WARN_ON, skip invalid slots in poll (count as invalid_buffers),
>> and advance the RX ring when remove_buffer_from_pool cannot map the
>> correlator. Rate-limit the bad correlator message.
>>
>> Complete NAPI when the interface is down or napi_disable is pending so
>> close/quiesce can finish. Do not restart_poll in that window. Close
>> keeps hypervisor IRQ disable before napi_disable (via
>> cleanup_rx_interrupts() / related cleanup helpers).
>>
>> Also validate descriptor length against skb tailroom before skb_put(),
>> and after napi_complete_done() on the budget-exhausted shutdown path
>> return a value less than budget so NAPI does not immediately reschedule.
> This patch looks very odd, like there's a bug somewhere and instead of
> fixing it we're making the rx path more resilient. BTW minor coding
> note - you're adding a bunch of heavily indented code to an already
> long function. Please consider factoring things out. Similar comment
> can be applied to other patches.
Agreed. The main fix here should be in the earlier resize/teardown path,
not in a trailing resilience patch.

I’ll fold that back into the owning resize work: drain before
deregister/unmap/free, publish the surviving queue range before freeing
queue resources, and use the same teardown path on the scale-up
enable_irq failure path. The poll-side skip logic should stay only as
belt-and-braces after the teardown fix, not as the primary answer.

I’ll also move the new poll branches into small helpers so
ibmveth_poll() stays a thin loop, but keep those helpers with the
patches that introduce the logic rather than as a standalone trailer
refactor.

I think the same cleanup principle applies to a few of the other
patches as well, so I’ll fold helper extraction into the owning changes
there too.

Thanks,
Mingming