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, 65 insertions, 0 deletions

diff --git a/rust/syn/span.rs b/rust/syn/span.rs
new file mode 100644
index 000000000..e6d55b3cc
--- /dev/null
+++ b/rust/syn/span.rs
@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use proc_macro2::extra::DelimSpan;
+use proc_macro2::{Delimiter, Group, Span, TokenStream};
+
+#[doc(hidden)]
+pub trait IntoSpans<S> {
+    fn into_spans(self) -> S;
+}
+
+impl IntoSpans<Span> for Span {
+    fn into_spans(self) -> Span {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 1]> for Span {
+    fn into_spans(self) -> [Span; 1] {
+        [self]
+    }
+}
+
+impl IntoSpans<[Span; 2]> for Span {
+    fn into_spans(self) -> [Span; 2] {
+        [self, self]
+    }
+}
+
+impl IntoSpans<[Span; 3]> for Span {
+    fn into_spans(self) -> [Span; 3] {
+        [self, self, self]
+    }
+}
+
+impl IntoSpans<[Span; 1]> for [Span; 1] {
+    fn into_spans(self) -> [Span; 1] {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 2]> for [Span; 2] {
+    fn into_spans(self) -> [Span; 2] {
+        self
+    }
+}
+
+impl IntoSpans<[Span; 3]> for [Span; 3] {
+    fn into_spans(self) -> [Span; 3] {
+        self
+    }
+}
+
+impl IntoSpans<DelimSpan> for Span {
+    fn into_spans(self) -> DelimSpan {
+        let mut group = Group::new(Delimiter::None, TokenStream::new());
+        group.set_span(self);
+        group.delim_span()
+    }
+}
+
+impl IntoSpans<DelimSpan> for DelimSpan {
+    fn into_spans(self) -> DelimSpan {
+        self
+    }
+}