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, 93 insertions, 0 deletions

diff --git a/drivers/block/rnbd/README b/drivers/block/rnbd/README
new file mode 100644
index 000000000..080f58a54
--- /dev/null
+++ b/drivers/block/rnbd/README
@@ -0,0 +1,93 @@
+********************************
+RDMA Network Block Device (RNBD)
+********************************
+
+Introduction
+------------
+
+RNBD (RDMA Network Block Device) is a pair of kernel modules
+(client and server) that allow for remote access of a block device on
+the server over RTRS protocol using the RDMA (InfiniBand, RoCE, iWARP)
+transport. After being mapped, the remote block devices can be accessed
+on the client side as local block devices.
+
+I/O is transferred between client and server by the RTRS transport
+modules. The administration of RNBD and RTRS modules is done via
+sysfs entries.
+
+Requirements
+------------
+
+  RTRS kernel modules
+
+Quick Start
+-----------
+
+Server side:
+  # modprobe rnbd_server
+
+Client side:
+  # modprobe rnbd_client
+  # echo "sessname=blya path=ip:10.50.100.66 device_path=/dev/ram0" > \
+            /sys/devices/virtual/rnbd-client/ctl/map_device
+
+  Where "sessname=" is a session name, a string to identify the session
+  on client and on server sides; "path=" is a destination IP address or
+  a pair of a source and a destination IPs, separated by comma.  Multiple
+  "path=" options can be specified in order to use multipath  (see RTRS
+  description for details); "device_path=" is the block device to be
+  mapped from the server side. After the session to the server machine is
+  established, the mapped device will appear on the client side under
+  /dev/rnbd<N>.
+
+
+RNBD-Server Module Parameters
+=============================
+
+dev_search_path
+---------------
+
+When a device is mapped from the client, the server generates the path
+to the block device on the server side by concatenating dev_search_path
+and the "device_path" that was specified in the map_device operation.
+
+The default dev_search_path is: "/".
+
+dev_search_path option can also contain %SESSNAME% in order to provide
+different device namespaces for different sessions.  See "device_path"
+option for details.
+
+============================
+Protocol (rnbd/rnbd-proto.h)
+============================
+
+1. Before mapping first device from a given server, client sends an
+RNBD_MSG_SESS_INFO to the server. Server responds with
+RNBD_MSG_SESS_INFO_RSP. Currently the messages only contain the protocol
+version for backward compatibility.
+
+2. Client requests to open a device by sending RNBD_MSG_OPEN message. This
+contains the path to the device and access mode (read-only or writable).
+Server responds to the message with RNBD_MSG_OPEN_RSP. This contains
+a 32 bit device id to be used for  IOs and device "geometry" related
+information: side, max_hw_sectors, etc.
+
+3. Client attaches RNBD_MSG_IO to each IO message send to a device. This
+message contains device id, provided by server in his rnbd_msg_open_rsp,
+sector to be accessed, read-write flags and bi_size.
+
+4. Client closes a device by sending RNBD_MSG_CLOSE which contains only the
+device id provided by the server.
+
+=========================================
+Contributors List(in alphabetical order)
+=========================================
+Danil Kipnis <danil.kipnis@profitbricks.com>
+Fabian Holler <mail@fholler.de>
+Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
+Jack Wang <jinpu.wang@profitbricks.com>
+Kleber Souza <kleber.souza@profitbricks.com>
+Lutz Pogrell <lutz.pogrell@cloud.ionos.com>
+Milind Dumbare <Milind.dumbare@gmail.com>
+Roman Penyaev <roman.penyaev@profitbricks.com>
+Swapnil Ingle <ingleswapnil@gmail.com>