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, 42 insertions, 0 deletions

diff --git a/Documentation/trace/events-pci-controller.rst b/Documentation/trace/events-pci-controller.rst
new file mode 100644
index 000000000..cb9f71592
--- /dev/null
+++ b/Documentation/trace/events-pci-controller.rst
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+.. SPDX-License-Identifier: GPL-2.0
+
+======================================
+Subsystem Trace Points: PCI Controller
+======================================
+
+Overview
+========
+The PCI controller tracing system provides tracepoints to monitor controller
+level information for debugging purpose. The events normally show up here:
+
+	/sys/kernel/tracing/events/pci_controller
+
+Cf. include/trace/events/pci_controller.h for the events definitions.
+
+Available Tracepoints
+=====================
+
+pcie_ltssm_state_transition
+---------------------------
+
+Monitors PCIe LTSSM state transition including state and rate information
+::
+
+    pcie_ltssm_state_transition  "dev: %s state: %s rate: %s\n"
+
+**Parameters**:
+
+* ``dev`` - PCIe controller instance
+* ``state`` - PCIe LTSSM state
+* ``rate`` - PCIe date rate
+
+**Example Usage**:
+
+.. code-block:: shell
+
+    # Enable the tracepoint
+    echo 1 > /sys/kernel/debug/tracing/events/pci_controller/pcie_ltssm_state_transition/enable
+
+    # Monitor events (the following output is generated when a device is linking)
+    cat /sys/kernel/debug/tracing/trace_pipe
+       kworker/0:0-9       [000] .....     5.600221: pcie_ltssm_state_transition: dev: a40000000.pcie state: RCVRY_EQ2 rate: 8.0 GT/s