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, 22 insertions, 0 deletions

diff --git a/include/net/aligned_data.h b/include/net/aligned_data.h
new file mode 100644
index 000000000..e1a1c8aed
--- /dev/null
+++ b/include/net/aligned_data.h
@@ -0,0 +1,22 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _NET_ALIGNED_DATA_H
+#define _NET_ALIGNED_DATA_H
+
+#include <linux/atomic.h>
+#include <linux/types.h>
+
+/* Structure holding cacheline aligned fields on SMP builds.
+ * Each field or group should have an ____cacheline_aligned_in_smp
+ * attribute to ensure no accidental false sharing can happen.
+ */
+struct net_aligned_data {
+	atomic64_t	net_cookie ____cacheline_aligned_in_smp;
+#if defined(CONFIG_INET)
+	atomic_long_t tcp_memory_allocated ____cacheline_aligned_in_smp;
+	atomic_long_t udp_memory_allocated ____cacheline_aligned_in_smp;
+#endif
+};
+
+extern struct net_aligned_data net_aligned_data;
+
+#endif /* _NET_ALIGNED_DATA_H */