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commit e2bb9e01d589f7fa82573aedd2765ff9b277816a upstream. Both bpf_trace_printk and bpf_trace_vprintk helpers use static buffer guarded with trace_printk_lock spin lock. The spin lock contention causes issues with bpf programs attached to contention_begin tracepoint [1][2]. Andrii suggested we could get rid of the contention by using trylock, but we could actually get rid of the spinlock completely by using percpu buffers the same way as for bin_args in bpf_bprintf_prepare function. Adding new return 'buf' argument to struct bpf_bprintf_data and making bpf_bprintf_prepare to return also the buffer for printk helpers. [1] https://lore.kernel.org/bpf/CACkBjsakT_yWxnSWr4r-0TpPvbKm9-OBmVUhJb7hV3hY8fdCkw@mail.gmail.com/ [2] https://lore.kernel.org/bpf/CACkBjsaCsTovQHFfkqJKto6S4Z8d02ud1D7MPESrHa1cVNNTrw@mail.gmail.com/ Reported-by: Hao Sun <sunhao.th@gmail.com> Suggested-by: Andrii Nakryiko <andrii@kernel.org> Signed-off-by: Jiri Olsa <jolsa@kernel.org> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Acked-by: Yonghong Song <yhs@fb.com> Link: https://lore.kernel.org/bpf/20221215214430.1336195-4-jolsa@kernel.org [cascardo: there is no bpf_trace_vprintk in 5.15] Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@igalia.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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.