Re: [PATCH v3] net/virtio-user: fix eventfd sharing in secondary process

Hello Samar,

On Fri, Jul 3, 2026 at 12:25 PM Samar Yadav <[email protected]> wrote:
>
> virtio_user secondary processes cannot communicate with the vhost
> backend: the kick/call eventfds are opened by the primary and never
> shared, so a secondary's queue notification writes to an invalid fd
> and traffic stalls.
>
> Share the fds over a dedicated virtio-user multiprocess channel. The
> primary registers a process-wide MP action that returns a port's
> kick/call fds (looked up by port name); a secondary requests them at
> probe time, before the port is announced.
>
> The received fds are stored in eth_dev->process_private, which is
> per-process, instead of the primary-owned shared dev->kickfds and
> dev->callfds arrays; the secondary data path notifies the backend using
> its own kickfd. In the primary, the MP handler reads the fd arrays under
> dev->mutex, and the teardown path takes the same lock while closing and
> freeing them, so the two cannot race.
>
> Also fix the pre-existing pthread_mutex_init(&dev->mutex, NULL) call in
> virtio_user_dev_init(): POSIX requires PTHREAD_PROCESS_SHARED for a mutex
> stored in shared memory regardless of which processes actually lock it;
> use rte_thread_mutex_init_shared() as other multiprocess-aware drivers do.
>
> Fixes: 1c8489da561b ("net/virtio-user: fix multi-process support")
> Cc: [email protected]
> Cc: [email protected]
>
> Signed-off-by: Samar Yadav <[email protected]>
> ---
> v3:
> - Reorder new #includes: system headers first, then DPDK lib headers
>   (alphabetized), then local virtio_* headers, per project convention.
> - Name the "2" in eventfd count/index arithmetic (kick + call per queue)
>   as VIRTIO_USER_EVENTFDS_PER_QUEUE instead of a bare literal. Leaves
>   the pre-existing max_queue_pairs * 2 vring math untouched, since that
>   is a different multiplier (vrings per queue pair) and already matches
>   this file's existing style.
> - Name the 5-second MP reply timeout in virtio_user_sync_eventfds() as
>   VIRTIO_USER_MP_TIMEOUT_SEC with a comment on the rationale.
>
> v2:
> - Use rte_calloc() instead of rte_malloc() for the kick/call fd arrays
>   in virtio_user_sync_eventfds() so allocation failures are cleaner and
>   unset entries are zero-initialised before the explicit -1 sentinel loop.
>   (Stephen Hemminger)
> - Fix the pre-existing pthread_mutex_init(&dev->mutex, NULL) call in
>   virtio_user_dev_init() to use rte_thread_mutex_init_shared(), which
>   sets PTHREAD_PROCESS_SHARED as POSIX requires for a mutex in shared
>   memory. Add #include <rte_thread.h> to pull in the declaration.
>   (Stephen Hemminger)
>
>  .mailmap                                      |   1 +
>  .../net/virtio/virtio_user/virtio_user_dev.c  |  59 +++-
>  .../net/virtio/virtio_user/virtio_user_dev.h  |  23 ++
>  drivers/net/virtio/virtio_user_ethdev.c       | 276 +++++++++++++++++-
>  4 files changed, 350 insertions(+), 9 deletions(-)
>

The patch looks good to me.

Reviewed-by: Maxime Coquelin <[email protected]>

Thanks,
Maxime