selftests/bpf: Test rhtab kptr cancellation semanticsgrafted

Resizable hash-map updates and deletions must not perform full special-field
destruction in their caller context. In particular, a referenced kptr must
remain attached to the allocation until the memory allocator destructor can
release it safely.

Add separate coverage for both affected paths. The update test stores a task
kptr, replaces the ordinary value bytes with BPF_EXIST, and verifies that the
kptr survived. The delete test removes an element and exchanges its kptr
through the still-valid map-value pointer before the allocation is reclaimed.

Both cases observe a NULL kptr when rhtab uses bpf_obj_free_fields(). They
recover and release the reference after rhtab switches to cancellation
semantics.

Signed-off-by: Nuoqi Gui <gnq25@mails.tsinghua.edu.cn>
[ kkd: Split update and delete coverage and rewrote the commit log ]
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904104203.345917-5-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 56 insertions, 0 deletions

diff --git a/include/net/psample.h b/include/net/psample.h
new file mode 100644
index 000000000..5071b5fc2
--- /dev/null
+++ b/include/net/psample.h
@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __NET_PSAMPLE_H
+#define __NET_PSAMPLE_H
+
+#include <uapi/linux/psample.h>
+#include <linux/list.h>
+
+struct psample_group {
+	struct list_head list;
+	struct net *net;
+	u32 group_num;
+	u32 refcount;
+	u32 seq;
+	struct rcu_head rcu;
+};
+
+struct psample_metadata {
+	u32 trunc_size;
+	int in_ifindex;
+	int out_ifindex;
+	u16 out_tc;
+	u64 out_tc_occ;	/* bytes */
+	u64 latency;	/* nanoseconds */
+	u8 out_tc_valid:1,
+	   out_tc_occ_valid:1,
+	   latency_valid:1,
+	   rate_as_probability:1,
+	   unused:4;
+	const u8 *user_cookie;
+	u32 user_cookie_len;
+};
+
+struct psample_group *psample_group_get(struct net *net, u32 group_num);
+void psample_group_take(struct psample_group *group);
+void psample_group_put(struct psample_group *group);
+
+struct sk_buff;
+
+#if IS_ENABLED(CONFIG_PSAMPLE)
+
+void psample_sample_packet(struct psample_group *group,
+			   const struct sk_buff *skb, u32 sample_rate,
+			   const struct psample_metadata *md);
+
+#else
+
+static inline void psample_sample_packet(struct psample_group *group,
+					 const struct sk_buff *skb,
+					 u32 sample_rate,
+					 const struct psample_metadata *md)
+{
+}
+
+#endif
+
+#endif /* __NET_PSAMPLE_H */