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, 35 insertions, 0 deletions

diff --git a/lib/test_module.c b/lib/test_module.c
new file mode 100644
index 000000000..3d1b29b74
--- /dev/null
+++ b/lib/test_module.c
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This module emits "Hello, world" on printk when loaded.
+ *
+ * It is designed to be used for basic evaluation of the module loading
+ * subsystem (for example when validating module signing/verification). It
+ * lacks any extra dependencies, and will not normally be loaded by the
+ * system unless explicitly requested by name.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/printk.h>
+
+static int __init test_module_init(void)
+{
+	pr_warn("Hello, world\n");
+
+	return 0;
+}
+
+module_init(test_module_init);
+
+static void __exit test_module_exit(void)
+{
+	pr_warn("Goodbye\n");
+}
+
+module_exit(test_module_exit);
+
+MODULE_AUTHOR("Kees Cook <keescook@chromium.org>");
+MODULE_DESCRIPTION("module loading subsystem test module");
+MODULE_LICENSE("GPL");