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Alexei reported crash by running test_progs -j on system with 32 cpus. It turned out the kprobe_multi bench test that attaches all ftrace-able functions will race with bpf_dispatcher_update, that calls bpf_arch_text_poke on bpf_dispatcher_xdp_func, which is ftrace-able function. Ftrace is not aware of this update so this will cause ftrace_bug with: WARNING: CPU: 6 PID: 1985 at arch/x86/kernel/ftrace.c:94 ftrace_verify_code+0x27/0x50 ... ftrace_replace_code+0xa3/0x170 ftrace_modify_all_code+0xbd/0x150 ftrace_startup_enable+0x3f/0x50 ftrace_startup+0x98/0xf0 register_ftrace_function+0x20/0x60 register_fprobe_ips+0xbb/0xd0 bpf_kprobe_multi_link_attach+0x179/0x430 __sys_bpf+0x18a1/0x2440 ... ------------[ ftrace bug ]------------ ftrace failed to modify [<ffffffff818d9380>] bpf_dispatcher_xdp_func+0x0/0x10 actual: ffffffe9:7b:ffffff9c:77:1e Setting ftrace call site to call ftrace function It looks like we need some way to hide some functions from ftrace, but meanwhile we workaround this by skipping bpf_dispatcher_xdp_func from kprobe_multi bench test. Reported-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Jiri Olsa <jolsa@kernel.org> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20220714082316.479181-1-jolsa@kernel.org
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.