Documentation: Fix typos

Fix typos in Documentation.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20230814212822.193684-4-helgaas@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation: bpf: Add missing line break separator in node_data struct code block

Stephen Rothwell reported htmldocs warning when merging bpf-next tree,
which was the same warning as reported by kernel test robot:

Documentation/bpf/graph_ds_impl.rst:62: ERROR: Error in "code-block" directive:
maximum 1 argument(s) allowed, 12 supplied.

The error is due to Sphinx confuses node_data struct declaration with
code-block directive option.

Fix the warning by separating the code-block marker with node_data struct
declaration.

Link: https://lore.kernel.org/linux-next/20230215144505.4751d823@canb.auug.org.au/
Link: https://lore.kernel.org/linux-doc/202302151123.wUE5FYFx-lkp@intel.com/
Fixes: c31315c3aa0929 ("bpf, documentation: Add graph documentation for non-owning refs")
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Bagas Sanjaya <bagasdotme@gmail.com>
Link: https://lore.kernel.org/r/20230215123253.41552-3-bagasdotme@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

bpf, documentation: Add graph documentation for non-owning refs

It is difficult to intuit the semantics of owning and non-owning
references from verifier code. In order to keep the high-level details
from being lost in the mailing list, this patch adds documentation
explaining semantics and details.

The target audience of doc added in this patch is folks working on BPF
internals, as there's focus on "what should the verifier do here". Via
reorganization or copy-and-paste, much of the content can probably be
repurposed for BPF program writer audience as well.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230214004017.2534011-9-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>