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Since bpf hash map was converted to use bpf_mem_alloc it is safe to use from tracing programs and in RT kernels. But per-cpu hash map is still using dynamic allocation for per-cpu map values, hence keep the warning for this map type. In the future alloc_percpu_gfp can be front-end-ed with bpf_mem_cache and this restriction will be completely lifted. perf_event (NMI) bpf programs have to use preallocated hash maps, because free_htab_elem() is using call_rcu which might crash if re-entered. Sleepable bpf programs have to use preallocated hash maps, because life time of the map elements is not protected by rcu_read_lock/unlock. This restriction can be lifted in the future as well. Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com> Acked-by: Andrii Nakryiko <andrii@kernel.org> Link: https://lore.kernel.org/bpf/20220902211058.60789-6-alexei.starovoitov@gmail.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.