[PATCH v2 9/9] bpf: add callback flag to skip multi-thread check

[Marat Khalili]

Add RTE_BPF_ETH_F_SKIP_MT_CHECK flag allowing callers to bypass the
suitability check when installing BPF packet callbacks.

This allows overriding rejections in cases where the port or queue is
configured with multi-thread capabilities (such as MT_LOCKFREE),
but the application guarantees that only one dataplane thread
accesses the queue at a time.

Update the unit test to verify that callback installation succeeds
when this flag is specified, and add a release note documenting the
restriction and the override flag.

Signed-off-by: Marat Khalili <qm2k21 at gmail.com>
---
 app/test/test_bpf.c                    | 20 ++++++++++++++++++++
 doc/guides/rel_notes/release_26_11.rst |  5 +++++
 lib/bpf/bpf_pkt.c                      |  8 +++++---
 lib/bpf/rte_bpf_ethdev.h               |  5 ++++-
 4 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/app/test/test_bpf.c b/app/test/test_bpf.c
index 02523984b5..0ab8aa8759 100644
--- a/app/test/test_bpf.c
+++ b/app/test/test_bpf.c
@@ -4692,7 +4692,27 @@ test_bpf_elf_tx_mt_lockfree(load_elf_image_t load_elf_image)
 		goto fail;
 	}
 
+	/* Tx installation must succeed when check is skipped with flag */
+	ret = rte_bpf_eth_tx_install(port, 0, bpf, RTE_BPF_ETH_F_SKIP_MT_CHECK);
+	if (ret != 0) {
+		printf("%s@%d: expected rte_bpf_eth_tx_install with SKIP_MT_CHECK to succeed, got %d\n",
+		       __func__, __LINE__, ret);
+		ret = TEST_FAILED;
+		goto fail;
+	}
+	rte_bpf_eth_tx_unload(port, 0);
+	bpf = NULL;
+
 	/* Rx installation on the same port must still succeed */
+	bpf = load_elf_image(app_test_bpf_filter_o, app_test_bpf_filter_o_len, "filter",
+			     NULL, 0, &prog_arg);
+	if (bpf == NULL) {
+		printf("%s@%d: failed to load BPF filter image\n",
+		       __func__, __LINE__);
+		ret = TEST_FAILED;
+		goto fail;
+	}
+
 	ret = rte_bpf_eth_rx_install(port, 0, bpf, 0);
 	if (ret != 0) {
 		printf("%s@%d: expected rte_bpf_eth_rx_install to succeed, got %d\n",
diff --git a/doc/guides/rel_notes/release_26_11.rst b/doc/guides/rel_notes/release_26_11.rst
index e282fa5581..a0a0161e39 100644
--- a/doc/guides/rel_notes/release_26_11.rst
+++ b/doc/guides/rel_notes/release_26_11.rst
@@ -366,6 +366,11 @@ API Changes
     ``rte_event_port_profile_links_get`` and
     ``rte_event_port_profile_unlink``
 
+* bpf: BPF packet callbacks can no longer be installed on
+  ``RTE_ETH_TX_OFFLOAD_MT_LOCKFREE`` ports and queues to prevent race
+  conditions on unload, but this safety feature can be overridden with
+  the new ``RTE_BPF_ETH_F_SKIP_MT_CHECK`` flag.
+
 * reorder: Promoted the following API from experimental to stable:
   ``rte_reorder_seqn``, ``rte_reorder_drain_up_to_seqn``,
   ``rte_reorder_min_seqn_set`` and ``rte_reorder_memory_footprint_get``.
diff --git a/lib/bpf/bpf_pkt.c b/lib/bpf/bpf_pkt.c
index 0b59ce22f1..7ccc8daa88 100644
--- a/lib/bpf/bpf_pkt.c
+++ b/lib/bpf/bpf_pkt.c
@@ -602,9 +602,11 @@ bpf_eth_elf_install(struct bpf_eth_cbh *cbh, uint16_t port, uint16_t queue,
 	if (bpf->prm.nb_prog_arg != 1)
 		return -EINVAL;
 
-	rc = bpf_eth_check_mt(cbh, port, queue);
-	if (rc != 0)
-		return rc;
+	if ((flags & RTE_BPF_ETH_F_SKIP_MT_CHECK) == 0) {
+		rc = bpf_eth_check_mt(cbh, port, queue);
+		if (rc != 0)
+			return rc;
+	}
 
 	if (cbh->type == BPF_ETH_RX)
 		frx = select_rx_callback(bpf->prm.prog_arg[0].type, flags);
diff --git a/lib/bpf/rte_bpf_ethdev.h b/lib/bpf/rte_bpf_ethdev.h
index cf3b4048f0..7a9f87e6cb 100644
--- a/lib/bpf/rte_bpf_ethdev.h
+++ b/lib/bpf/rte_bpf_ethdev.h
@@ -13,7 +13,8 @@
  * - in the data plane, it expects only one thread per port/queue pair at a time.
  *   Calling RX/TX burst functions concurrently on the same queue (e.g. when using
  *   RTE_ETH_TX_OFFLOAD_MT_LOCKFREE, shared RX queues, or multi-threaded
- *   software PMDs) is not supported.
+ *   software PMDs) is not supported and will be rejected at installation time
+ *   unless overridden by RTE_BPF_ETH_F_SKIP_MT_CHECK.
  * - in the control plane, it is not MT safe, i.e. it is not allowed to do
  *   load/unload for the same port/queue from different threads in parallel.
  * - though it allows load/unload at runtime
@@ -37,6 +38,8 @@ extern "C" {
 enum {
 	RTE_BPF_ETH_F_NONE = 0,
 	RTE_BPF_ETH_F_JIT  = 0x1, /**< use compiled into native ISA code */
+	RTE_BPF_ETH_F_SKIP_MT_CHECK = 0x2,
+	/**< skip check for concurrent data plane thread usage */
 };
 
 /**
-- 
2.43.0