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>

3 files changed, 92 insertions, 0 deletions

diff --git a/rust/proc-macro2/probe/proc_macro_span.rs b/rust/proc-macro2/probe/proc_macro_span.rs
new file mode 100644
index 000000000..892a7eb3e
--- /dev/null
+++ b/rust/proc-macro2/probe/proc_macro_span.rs
@@ -0,0 +1,53 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// This code exercises the surface area that we expect of Span's unstable API.
+// If the current toolchain is able to compile it, then proc-macro2 is able to
+// offer these APIs too.
+
+#![cfg_attr(procmacro2_build_probe, feature(proc_macro_span))]
+
+extern crate proc_macro;
+
+use core::ops::{Range, RangeBounds};
+use proc_macro::{Literal, Span};
+use std::path::PathBuf;
+
+pub fn byte_range(this: &Span) -> Range<usize> {
+    this.byte_range()
+}
+
+pub fn start(this: &Span) -> Span {
+    this.start()
+}
+
+pub fn end(this: &Span) -> Span {
+    this.end()
+}
+
+pub fn line(this: &Span) -> usize {
+    this.line()
+}
+
+pub fn column(this: &Span) -> usize {
+    this.column()
+}
+
+pub fn file(this: &Span) -> String {
+    this.file()
+}
+
+pub fn local_file(this: &Span) -> Option<PathBuf> {
+    this.local_file()
+}
+
+pub fn join(this: &Span, other: Span) -> Option<Span> {
+    this.join(other)
+}
+
+pub fn subspan<R: RangeBounds<usize>>(this: &Literal, range: R) -> Option<Span> {
+    this.subspan(range)
+}
+
+// Include in sccache cache key.
+#[cfg(procmacro2_build_probe)]
+const _: Option<&str> = option_env!("RUSTC_BOOTSTRAP");
diff --git a/rust/proc-macro2/probe/proc_macro_span_file.rs b/rust/proc-macro2/probe/proc_macro_span_file.rs
new file mode 100644
index 000000000..f2dbc4056
--- /dev/null
+++ b/rust/proc-macro2/probe/proc_macro_span_file.rs
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// The subset of Span's API stabilized in Rust 1.88.
+
+extern crate proc_macro;
+
+use proc_macro::Span;
+use std::path::PathBuf;
+
+pub fn file(this: &Span) -> String {
+    this.file()
+}
+
+pub fn local_file(this: &Span) -> Option<PathBuf> {
+    this.local_file()
+}
diff --git a/rust/proc-macro2/probe/proc_macro_span_location.rs b/rust/proc-macro2/probe/proc_macro_span_location.rs
new file mode 100644
index 000000000..ae19c9339
--- /dev/null
+++ b/rust/proc-macro2/probe/proc_macro_span_location.rs
@@ -0,0 +1,23 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+// The subset of Span's API stabilized in Rust 1.88.
+
+extern crate proc_macro;
+
+use proc_macro::Span;
+
+pub fn start(this: &Span) -> Span {
+    this.start()
+}
+
+pub fn end(this: &Span) -> Span {
+    this.end()
+}
+
+pub fn line(this: &Span) -> usize {
+    this.line()
+}
+
+pub fn column(this: &Span) -> usize {
+    this.column()
+}