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, 15 insertions, 0 deletions

diff --git a/tools/lib/zalloc.c b/tools/lib/zalloc.c
new file mode 100644
index 000000000..9c856d59f
--- /dev/null
+++ b/tools/lib/zalloc.c
@@ -0,0 +1,15 @@
+// SPDX-License-Identifier: LGPL-2.1
+
+#include <stdlib.h>
+#include <linux/zalloc.h>
+
+void *zalloc(size_t size)
+{
+	return calloc(1, size);
+}
+
+void __zfree(void **ptr)
+{
+	free(*ptr);
+	*ptr = NULL;
+}