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, 69 insertions, 0 deletions

diff --git a/rust/helpers/bitops.c b/rust/helpers/bitops.c
new file mode 100644
index 000000000..271b8a712
--- /dev/null
+++ b/rust/helpers/bitops.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/bitops.h>
+#include <linux/find.h>
+
+__rust_helper
+void rust_helper___set_bit(unsigned long nr, unsigned long *addr)
+{
+	__set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper___clear_bit(unsigned long nr, unsigned long *addr)
+{
+	__clear_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_set_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	set_bit(nr, addr);
+}
+
+__rust_helper
+void rust_helper_clear_bit(unsigned long nr, volatile unsigned long *addr)
+{
+	clear_bit(nr, addr);
+}
+
+/*
+ * The rust_helper_ prefix is intentionally omitted below so that the
+ * declarations in include/linux/find.h are compatible with these helpers.
+ *
+ * Note that the below #ifdefs mean that the helper is only created if C does
+ * not provide a definition.
+ */
+#ifdef find_first_zero_bit
+__rust_helper
+unsigned long _find_first_zero_bit(const unsigned long *p, unsigned long size)
+{
+	return find_first_zero_bit(p, size);
+}
+#endif /* find_first_zero_bit */
+
+#ifdef find_next_zero_bit
+__rust_helper
+unsigned long _find_next_zero_bit(const unsigned long *addr,
+				  unsigned long size, unsigned long offset)
+{
+	return find_next_zero_bit(addr, size, offset);
+}
+#endif /* find_next_zero_bit */
+
+#ifdef find_first_bit
+__rust_helper
+unsigned long _find_first_bit(const unsigned long *addr, unsigned long size)
+{
+	return find_first_bit(addr, size);
+}
+#endif /* find_first_bit */
+
+#ifdef find_next_bit
+__rust_helper
+unsigned long _find_next_bit(const unsigned long *addr, unsigned long size,
+			     unsigned long offset)
+{
+	return find_next_bit(addr, size, offset);
+}
+#endif /* find_next_bit */