[PATCH 6/9] bpf: simplify callback inuse tracking to boolean flag

[Stephen Hemminger]

On Sun, 11 Oct 2026 18:21:54 +0000
Marat Khalili <qm2k21 at gmail.com> wrote:

> --- a/lib/bpf/bpf_pkt.c
> +++ b/lib/bpf/bpf_pkt.c
> @@ -36,12 +36,12 @@
>   * 2. Member `cb` of struct `bpf_eth_cbi`;
>   * 3. Member `use` of struct `bpf_eth_cbi`;
>   *
> - * BPF program is only executed if the first two are set, and increments `use` at the start and
> - * end of the callback execution so that in the safe state its value is even.
> + * BPF program is only executed if the first two are set, and sets `use` to 1 at the start and
> + * to 0 at the end of the callback execution.
>   * This relies on only one thread calling the per-port/queue callback at a time.
>   *
>   * Unload processing starts with clearing the first two entities,
> - * then waits for `use` to become even before destroying the BPF program.
> + * then waits for `use` to become 0 before destroying the BPF program.
>   * The whole operation is protected by a control-plane-only spinlock (not shown on the diagram).
>   *
>   * Typical sequence of synchronization actions between CP and DP on unload is shown below:
> @@ -52,7 +52,7 @@
>   *     |                      |               |              |              |                |
>   *     |                      |<---------------------- fetch callback -----------------------|
>   *     |                      |               |              |              |                |
> - *     |                      |               |<------------- increment to odd --------------|
> + *     |                      |               |<------------- store 1 -----------------------|
>   *     |                      |               |              |              |                |
>   *     |-- remove callback -->|               |              |              |       rte_smp_mb()
>   *     |                      |               |              |              |                |
> @@ -62,17 +62,17 @@
>   *     |                      |               |              |              |                |
>   *   rte_smp_mb()             |               |              |              |                |
>   *     |                      |               |              |              |                |
> - *     +-if use is odd        |               |              |              | if cb not NULL-+
> + *     +-while use is 1       |               |              |              | if cb not NULL-+
>   *     | |                    |               |              |              |              | |
> - *     | +------------ fetch odd ------------>|              |              |<-- execute --+ |
> + *     | +------------ fetch 1 -------------->|              |              |<-- execute --+ |
>   *     | |                    |               |              |              |  BPF program | |
> - *     | +-while use is same  |               |              |              |              +-+
> - *     | | |                  |               |              |              |                |
> - *     | | +---------- fetch odd ------------>|              |              |      rte_smp_rmb()
> - *     | | |                  |               |              |              |                |
> - *     +-+-+                  |               |<------------- increment to even -------------|
> + *     | |                    |               |              |              |              +-+
> + *     | |                    |               |              |              |                |
> + *     | |                    |               |              |              |      rte_smp_rmb()
> + *     | |                    |               |              |              |                |
> + *     +-+                    |               |<------------- store 0 -----------------------|
>   *     |                      |               |              |              |                |
> - *     |------------- fetch even ------------>|              |              |                |
> + *     |------------- fetch 0 --------------->|              |              |                |
>   *     |                      |               |              |              |                |
>   *     |----------------- destroy BPF program and cleanup ----------------->|                |
>   *     |                      |               |              |              |                |
> @@ -87,7 +87,7 @@
>   */
>  struct __rte_cache_aligned bpf_eth_cbi {
>  	/* used by both data & control path */
> -	RTE_ATOMIC(uint32_t) use;    /*usage counter */
> +	RTE_ATOMIC(uint32_t) use;    /* usage flag: 1 when in use, 0 otherwise */

If it is only on/off now make it a bool.