On 15 Jan 2026, at 20:54, Aaron Conole wrote:
> During code-review, it seems like it could be possible to publish a
> flow into the cmap, and the hw offload thread assistance could miss
> the appropriate flow. This situation probably didn't occur much in
> practice, and the result might be just a dropped packet (although, I'm
> not sure that it couldn't also result in a weird duplicate flow
> getting installed due to the check in mark_to_flow_find that gets
> called during dfc_processing).
>
> This change reorders the assignment to before the cmap_insert. The
> cmap_insert should act as a barrier in this case to ensure that the
> write to flow->mark is ready before the read (after the
> CMAP_FOR_EACH_WITH_HASH).
>
> Fixes: 241bad15d99a ("dpif-netdev: associate flow with a mark id")
> Signed-off-by: Aaron Conole <[email protected]>
Hi Aaron,
I haven’t reviewed the code yet, but it should be noted that this does not
apply to main after the offload series was merged. So this would be for older
streams only, right?
Cheers,
Eelco
> ---
> lib/dpif-netdev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c
> index 224ce7086f..31b95f153c 100644
> --- a/lib/dpif-netdev.c
> +++ b/lib/dpif-netdev.c
> @@ -2600,10 +2600,10 @@ mark_to_flow_associate(const uint32_t mark, struct
> dp_netdev_flow *flow)
> unsigned int tid = netdev_offload_thread_id();
> dp_netdev_flow_ref(flow);
>
> + flow->mark = mark;
> cmap_insert(&dp_offload_threads[tid].mark_to_flow,
> CONST_CAST(struct cmap_node *, &flow->mark_node),
> hash_int(mark, 0));
> - flow->mark = mark;
>
> VLOG_DBG("Associated dp_netdev flow %p with mark %u mega_ufid "UUID_FMT,
> flow, mark, UUID_ARGS((struct uuid *) &flow->mega_ufid));
> --
> 2.51.0
>
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