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, 57 insertions, 0 deletions

diff --git a/rust/helpers/task.c b/rust/helpers/task.c
new file mode 100644
index 000000000..b46b1433a
--- /dev/null
+++ b/rust/helpers/task.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/kernel.h>
+#include <linux/sched/task.h>
+
+__rust_helper void rust_helper_might_resched(void)
+{
+	might_resched();
+}
+
+__rust_helper struct task_struct *rust_helper_get_current(void)
+{
+	return current;
+}
+
+__rust_helper void rust_helper_get_task_struct(struct task_struct *t)
+{
+	get_task_struct(t);
+}
+
+__rust_helper void rust_helper_put_task_struct(struct task_struct *t)
+{
+	put_task_struct(t);
+}
+
+__rust_helper kuid_t rust_helper_task_uid(struct task_struct *task)
+{
+	return task_uid(task);
+}
+
+#ifndef CONFIG_USER_NS
+__rust_helper uid_t rust_helper_from_kuid(struct user_namespace *to, kuid_t uid)
+{
+	return from_kuid(to, uid);
+}
+#endif /* CONFIG_USER_NS */
+
+__rust_helper bool rust_helper_uid_eq(kuid_t left, kuid_t right)
+{
+	return uid_eq(left, right);
+}
+
+__rust_helper kuid_t rust_helper_current_euid(void)
+{
+	return current_euid();
+}
+
+__rust_helper struct user_namespace *rust_helper_current_user_ns(void)
+{
+	return current_user_ns();
+}
+
+__rust_helper pid_t rust_helper_task_tgid_nr_ns(struct task_struct *tsk,
+						struct pid_namespace *ns)
+{
+	return task_tgid_nr_ns(tsk, ns);
+}