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, 42 insertions, 0 deletions

diff --git a/samples/livepatch/livepatch-callbacks-mod.c b/samples/livepatch/livepatch-callbacks-mod.c
new file mode 100644
index 000000000..d1851b471
--- /dev/null
+++ b/samples/livepatch/livepatch-callbacks-mod.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Copyright (C) 2017 Joe Lawrence <joe.lawrence@redhat.com>
+ */
+
+/*
+ * livepatch-callbacks-mod.c - (un)patching callbacks demo support module
+ *
+ *
+ * Purpose
+ * -------
+ *
+ * Simple module to demonstrate livepatch (un)patching callbacks.
+ *
+ *
+ * Usage
+ * -----
+ *
+ * This module is not intended to be standalone.  See the "Usage"
+ * section of livepatch-callbacks-demo.c.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+
+static int livepatch_callbacks_mod_init(void)
+{
+	pr_info("%s\n", __func__);
+	return 0;
+}
+
+static void livepatch_callbacks_mod_exit(void)
+{
+	pr_info("%s\n", __func__);
+}
+
+module_init(livepatch_callbacks_mod_init);
+module_exit(livepatch_callbacks_mod_exit);
+MODULE_DESCRIPTION("Live patching demo for (un)patching callbacks, support module");
+MODULE_LICENSE("GPL");