[PATCH RESEND v3 0/3] bpf/verifier: Expand the usage scenarios of bpf_kptr_xchg

[Chengkaitao <pilgrimtao@gmail.com>]

From: Chengkaitao <chengkaitao@kylinos.cn>

When using bpf_kptr_xchg, we triggered the following error:
    31: (85) call bpf_kptr_xchg#194
    function calls are not allowed while holding a lock
bpf_kptr_xchg can now be used in lock-held contexts, so we extended
its usage scope in [patch 1/2].

When writing test cases using bpf_kptr_xchg and bpf_rbtree_*, the
following approach must be followed:

	bpf_spin_lock(&lock);
	rb_n = bpf_rbtree_root(&root);
	while (rb_n && can_loop) {
		rb_n = bpf_rbtree_remove(&root, rb_n);
		if (!rb_n)
			goto fail;

		tnode = container_of(rb_n, struct tree_node, node);
		node_data = bpf_kptr_xchg(&tnode->node_data, NULL);
		if (!node_data)
			goto fail;

		data = node_data->data;
		/* use data to do something */

		node_data = bpf_kptr_xchg(&tnode->node_data, node_data);
		if (node_data)
			goto fail;

		bpf_rbtree_add(&root, rb_n, less);

		if (lookup_key < tnode->key)
			rb_n = bpf_rbtree_left(&root, rb_n);
		else
			rb_n = bpf_rbtree_right(&root, rb_n);
	}
	bpf_spin_unlock(&lock);

The above illustrates a lock-remove-read-add-unlock workflow, which
exhibits lower performance. To address this, we introduced support
for a streamlined lock-read-unlock operation in [patch 2/2].

Changes in v3:
- Fix compilation errors
Changes in v2:
- Allow using bpf_kptr_xchg even if the NON_OWN_REF flag is set
- Add test case

Link to V2:
https://lore.kernel.org/all/20260201031607.32940-1-pilgrimtao@gmail.com/
Link to V1:
https://lore.kernel.org/all/20260122081426.78472-1-pilgrimtao@gmail.com/

Chengkaitao (3):
  bpf/verifier: allow calling bpf_kptr_xchg while holding a lock
  bpf/verifier: allow using bpf_kptr_xchg even if the NON_OWN_REF flag
    is set
  selftests/bpf: Add supplementary tests for bpf_kptr_xchg

 kernel/bpf/verifier.c                         |   7 +-
 .../testing/selftests/bpf/prog_tests/rbtree.c |   6 +
 tools/testing/selftests/bpf/progs/bpf_misc.h  |   4 +
 .../selftests/bpf/progs/rbtree_search_kptr.c  | 164 ++++++++++++++++++
 4 files changed, 179 insertions(+), 2 deletions(-)
 create mode 100644 tools/testing/selftests/bpf/progs/rbtree_search_kptr.c

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