Re: [PATCH v3 01/29] bpf: replace deprecated SMP barriers with C11 fences

[Marat Khalili <qm2k21@gmail.com>]

On 13/10/2026 08:54, David Marchand wrote:
> This blocks the SMP barrier removal for rc1.
>
> What is your proposal?
>
> I think it makes sense to take
> https://patchwork.dpdk.org/project/dpdk/list/?series=39599 first, then
> resolve the conflict for the patch from this thread.
> Is this BPF series ready for merge?
>
> If it is not ready yet, what should be done on the current patch?
> Is a s/rte_smp_rmb()/rte_atomic_thread_fence(rte_memory_order_seq_cst)/ enough?
> The commitlog would also need some rewritting.

I think we should be able to unblock this patchset with the diff below. 
Last version contains some additional out-of-scope changes that might 
not be helpful in the long run, but I tend to believe Stephen and 
Wathsala that they are not breaking anything (I have not checked it 
myself). If the version below is ok with Stephen I would prefer it 
(consider it acked), otherwise I can withdraw my NAK for the sake of the 
release, at the cost of some potentially confusing noise in the commit 
history in the future.

diff --git a/lib/bpf/bpf_pkt.c b/lib/bpf/bpf_pkt.c
index f072fdaaed..0d0c37cdc5 100644
--- a/lib/bpf/bpf_pkt.c
+++ b/lib/bpf/bpf_pkt.c
@@ -82,7 +82,7 @@ bpf_eth_cbi_inuse(struct bpf_eth_cbi *cbi)
  {
         cbi->use++;
         /* make sure no store/load reordering could happen */
-       rte_smp_mb();
+       rte_atomic_thread_fence(rte_memory_order_seq_cst);
  }

  /*
@@ -92,7 +92,7 @@ static __rte_always_inline void
  bpf_eth_cbi_unuse(struct bpf_eth_cbi *cbi)
  {
         /* make sure all previous loads are completed */
-       rte_smp_rmb();
+       rte_atomic_thread_fence(rte_memory_order_release);
         cbi->use++;
  }

@@ -105,7 +105,7 @@ bpf_eth_cbi_wait(const struct bpf_eth_cbi *cbi)
         uint32_t puse;

         /* make sure all previous loads and stores are completed */
-       rte_smp_mb();
+       rte_atomic_thread_fence(rte_memory_order_seq_cst);

         puse = cbi->use;

@@ -439,7 +439,7 @@ bpf_eth_cbi_unload(struct bpf_eth_cbi *bc)
  {
         /* mark this cbi as empty */
         bc->cb = NULL;
-       rte_smp_mb();
+       rte_atomic_thread_fence(rte_memory_order_seq_cst);

         /* make sure datapath doesn't use bpf anymore, then destroy bpf */
         bpf_eth_cbi_wait(bc);