selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 22 insertions, 0 deletions

diff --git a/tools/verification/models/stall.dot b/tools/verification/models/stall.dot
new file mode 100644
index 000000000..50077d1df
--- /dev/null
+++ b/tools/verification/models/stall.dot
@@ -0,0 +1,22 @@
+digraph state_automaton {
+	center = true;
+	size = "7,11";
+	{node [shape = circle] "enqueued"};
+	{node [shape = plaintext, style=invis, label=""] "__init_dequeued"};
+	{node [shape = doublecircle] "dequeued"};
+	{node [shape = circle] "running"};
+	"__init_dequeued" -> "dequeued";
+	"enqueued" [label = "enqueued\nclk < threshold_jiffies"];
+	"running" [label = "running"];
+	"dequeued" [label = "dequeued", color = green3];
+	"running" -> "running" [ label = "sched_switch_in\nsched_wakeup" ];
+	"enqueued" -> "enqueued" [ label = "sched_wakeup" ];
+	"enqueued" -> "running" [ label = "sched_switch_in" ];
+	"running" -> "dequeued" [ label = "sched_switch_wait" ];
+	"dequeued" -> "enqueued" [ label = "sched_wakeup;reset(clk)" ];
+	"running" -> "enqueued" [ label = "sched_switch_preempt;reset(clk)" ];
+	{ rank = min ;
+		"__init_dequeued";
+		"dequeued";
+	}
+}