RE: [EXTERNAL] Re: [PATCH v2 3/8] net/netvsc: add multi-process VF device removal support

Long Li
2026-02-23T22:32:57Z

> Subject: [EXTERNAL] Re: [PATCH v2 3/8] net/netvsc: add multi-process VF device
> removal support
>
> On Fri, 20 Feb 2026 18:45:22 -0800
> longli@linux.microsoft.com wrote:
>
> > From: Long Li <longli@microsoft.com>
> >
> > When a VF device is hot-removed by the primary process, secondary
> > processes must be notified to release their references to the VF port.
> > Without this, secondary processes retain stale port references leading
> > to crashes or undefined behavior when accessing the removed device.
> >
> > This patch adds multi-process communication infrastructure to
> > coordinate VF removal across all processes:
> >
> > - Shared memory (netvsc_shared_data) to track secondary process count
> > - Multi-process message handlers (NETVSC_MP_REQ_VF_REMOVE) to notify
> > secondaries when primary removes a VF device
> > - Secondary handler calls rte_eth_dev_release_port() to cleanly release
> > the VF port in its own process space
> > - Primary waits for all secondaries to acknowledge removal before
> > proceeding
> >
> > The implementation uses rte_mp_request_sync() to ensure all secondary
> > processes respond within NETVSC_MP_REQ_TIMEOUT_SEC (5 seconds) before
> > the primary completes the VF removal sequence.
> >
> > Fixes: 7fc4c0997b04 ("net/netvsc: fix hot adding multiple VF PCI
> > devices")
> > Cc: stable@dpdk.org
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
>
> AI review feedback:
>
> **Patch 3 (net/netvsc: add multi-process VF device removal support)** — adds
> MP infrastructure to coordinate VF removal across processes.
>
> **Three concerns:**
>
> 1. **Race window on `secondary_cnt` during probe (~50% confidence).** The
> secondary increments `secondary_cnt` *after* `rte_eth_dev_probing_finish()`,
> but `netvsc_init_once()` and device setup happen before that. A primary
> removing a VF during this window sees `secondary_cnt == 0`, skips
> `rte_mp_request_sync()`, and the secondary never gets notified — leaving it with
> a stale VF port reference.
>
> 2. **Misleading "VF is already locked by primary" comment.** In
> `netvsc_secondary_handle_device_remove()`, the code reads `hv->vf_ctx.vf_port`
> from shared memory with a comment saying the primary's lock protects it. But
> `rte_rwlock_t` is process-local — it doesn't work cross-process. The actual
> synchronization comes from the MP message exchange itself (the primary sends
> the message after setting state, the secondary handles it after receiving). The
> comment should reflect that.
>
> 3. **`netvsc_init_once()` not protected by the spinlock.** It's called from
> `eth_hn_probe()` without `netvsc_shared_data_lock`, while
> `netvsc_uninit_once()` is called *inside* the lock. If two netvsc devices probe
> concurrently in the same process, the `init_done` flag check could race. Low risk
> since DPDK probe is typically single-threaded, but inconsistent with the uninit
> path.
>
> **Minor style notes:** `MZ_NETVSC_SHARED_DATA` uses macro-style naming
> but is a `const char *` variable — could be a `#define` for consistency with
> `NETVSC_MP_NAME`. The stub `netvsc_mp_primary_handle()` that always
> returns 0 is benign but could mask future protocol errors.
>
> **Overall:** Sound infrastructure, suitable for merging with the comment fix and
> awareness of the probe-time race window.

I'm sending v3 addressing those comments.

Thanks,
Long