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, 38 insertions, 0 deletions

diff --git a/io_uring/sqpoll.h b/io_uring/sqpoll.h
new file mode 100644
index 000000000..fd2f6f29b
--- /dev/null
+++ b/io_uring/sqpoll.h
@@ -0,0 +1,38 @@
+// SPDX-License-Identifier: GPL-2.0
+
+struct io_sq_data {
+	refcount_t		refs;
+	atomic_t		park_pending;
+	struct mutex		lock;
+
+	/* ctx's that are using this sqd */
+	struct list_head	ctx_list;
+
+	struct task_struct __rcu *thread;
+	struct wait_queue_head	wait;
+
+	unsigned		sq_thread_idle;
+	int			sq_cpu;
+	pid_t			task_pid;
+	pid_t			task_tgid;
+
+	u64			work_time;
+	unsigned long		state;
+	struct completion	exited;
+};
+
+int io_sq_offload_create(struct io_ring_ctx *ctx, struct io_uring_params *p);
+void io_sq_thread_finish(struct io_ring_ctx *ctx);
+void io_sq_thread_stop(struct io_sq_data *sqd);
+void io_sq_thread_park(struct io_sq_data *sqd);
+void io_sq_thread_unpark(struct io_sq_data *sqd);
+void io_put_sq_data(struct io_sq_data *sqd);
+void io_sqpoll_wait_sq(struct io_ring_ctx *ctx);
+int io_sqpoll_wq_cpu_affinity(struct io_ring_ctx *ctx, cpumask_var_t mask);
+u64 io_sq_cpu_usec(struct task_struct *tsk);
+
+static inline struct task_struct *sqpoll_task_locked(struct io_sq_data *sqd)
+{
+	return rcu_dereference_protected(sqd->thread,
+					 lockdep_is_held(&sqd->lock));
+}