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Martin KaFai Lau says: ==================== From: Martin KaFai Lau <martin.lau@kernel.org> The struct_ops is sharing the tracing-trampoline's enter/exit function which tracks prog->active to avoid recursion. It turns out the struct_ops bpf prog will hit this prog->active and unnecessarily skipped running the struct_ops prog. eg. The '.ssthresh' may run in_task() and then interrupted by softirq that runs the same '.ssthresh'. The kernel does not call the tcp-cc's ops in a recursive way, so this set is to remove the recursion check for struct_ops prog. v3: - Clear the bpf_chg_cc_inprogress from the newly cloned tcp_sock in tcp_create_openreq_child() because the listen sk can be cloned without lock being held. (Eric Dumazet) v2: - v1 [0] turned into a long discussion on a few cases and also whether it needs to follow the bpf_run_ctx chain if there is tracing bpf_run_ctx (kprobe/trace/trampoline) running in between. It is a good signal that it is not obvious enough to reason about it and needs a tradeoff for a more straight forward approach. This revision uses one bit out of an existing 1 byte hole in the tcp_sock. It is in Patch 4. [0]: https://lore.kernel.org/bpf/20220922225616.3054840-1-kafai@fb.com/T/#md98d40ac5ec295fdadef476c227a3401b2b6b911 ==================== Signed-off-by: Alexei Starovoitov <ast@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.