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Masahiro Yamada 87c7ee67de scripts: handle BrokenPipeError for python scripts In the follow-up of commit `fb3041d61f` ("kbuild: fix SIGPIPE error message for AR=gcc-ar and AR=llvm-ar"), Kees Cook pointed out that tools should _not_ catch their own SIGPIPEs [1] [2]. Based on his feedback, LLVM was fixed [3]. However, Python's default behavior is to show noisy bracktrace when SIGPIPE is sent. So, scripts written in Python are basically in the same situation as the buggy llvm tools. Example: $ make -s allnoconfig $ make -s allmodconfig $ scripts/diffconfig .config.old .config \| head -n1 -ALIX n Traceback (most recent call last): File "/home/masahiro/linux/scripts/diffconfig", line 132, in <module> main() File "/home/masahiro/linux/scripts/diffconfig", line 130, in main print_config("+", config, None, b[config]) File "/home/masahiro/linux/scripts/diffconfig", line 64, in print_config print("+%s %s" % (config, new_value)) BrokenPipeError: [Errno 32] Broken pipe Python documentation [4] notes how to make scripts die immediately and silently: """ Piping output of your program to tools like head(1) will cause a SIGPIPE signal to be sent to your process when the receiver of its standard output closes early. This results in an exception like BrokenPipeError: [Errno 32] Broken pipe. To handle this case, wrap your entry point to catch this exception as follows: import os import sys def main(): try: # simulate large output (your code replaces this loop) for x in range(10000): print("y") # flush output here to force SIGPIPE to be triggered # while inside this try block. sys.stdout.flush() except BrokenPipeError: # Python flushes standard streams on exit; redirect remaining output # to devnull to avoid another BrokenPipeError at shutdown devnull = os.open(os.devnull, os.O_WRONLY) os.dup2(devnull, sys.stdout.fileno()) sys.exit(1) # Python exits with error code 1 on EPIPE if __name__ == '__main__': main() Do not set SIGPIPE’s disposition to SIG_DFL in order to avoid BrokenPipeError. Doing that would cause your program to exit unexpectedly whenever any socket connection is interrupted while your program is still writing to it. """ Currently, tools/perf/scripts/python/intel-pt-events.py seems to be the only script that fixes the issue that way. tools/perf/scripts/python/compaction-times.py uses another approach signal.signal(signal.SIGPIPE, signal.SIG_DFL) but the Python documentation clearly says "Don't do it". I cannot fix all Python scripts since there are so many. I fixed some in the scripts/ directory. [1]: https://lore.kernel.org/all/202211161056.1B9611A@keescook/ [2]: https://github.com/llvm/llvm-project/issues/59037 [3]: `4787efa380` [4]: https://docs.python.org/3/library/signal.html#note-on-sigpipe Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nick Desaulniers <ndesaulniers@google.com> Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>	2023-01-26 12:43:33 +09:00
..
gen_compile_commands.py	kbuild: rename cmd_$@ to savedcmd_$@ in *.cmd files	2023-01-22 23:43:33 +09:00
run-clang-tools.py	scripts: handle BrokenPipeError for python scripts	2023-01-26 12:43:33 +09:00

Masahiro Yamada 87c7ee67de scripts: handle BrokenPipeError for python scripts

In the follow-up of commit fb3041d61f ("kbuild: fix SIGPIPE error
message for AR=gcc-ar and AR=llvm-ar"), Kees Cook pointed out that
tools should _not_ catch their own SIGPIPEs [1] [2].

Based on his feedback, LLVM was fixed [3].

However, Python's default behavior is to show noisy bracktrace when
SIGPIPE is sent. So, scripts written in Python are basically in the
same situation as the buggy llvm tools.

Example:

  $ make -s allnoconfig
  $ make -s allmodconfig
  $ scripts/diffconfig .config.old .config | head -n1
  -ALIX n
  Traceback (most recent call last):
    File "/home/masahiro/linux/scripts/diffconfig", line 132, in <module>
      main()
    File "/home/masahiro/linux/scripts/diffconfig", line 130, in main
      print_config("+", config, None, b[config])
    File "/home/masahiro/linux/scripts/diffconfig", line 64, in print_config
      print("+%s %s" % (config, new_value))
  BrokenPipeError: [Errno 32] Broken pipe

Python documentation [4] notes how to make scripts die immediately and
silently:

  """
  Piping output of your program to tools like head(1) will cause a
  SIGPIPE signal to be sent to your process when the receiver of its
  standard output closes early. This results in an exception like
  BrokenPipeError: [Errno 32] Broken pipe. To handle this case,
  wrap your entry point to catch this exception as follows:

    import os
    import sys

    def main():
        try:
            # simulate large output (your code replaces this loop)
            for x in range(10000):
                print("y")
            # flush output here to force SIGPIPE to be triggered
            # while inside this try block.
            sys.stdout.flush()
        except BrokenPipeError:
            # Python flushes standard streams on exit; redirect remaining output
            # to devnull to avoid another BrokenPipeError at shutdown
            devnull = os.open(os.devnull, os.O_WRONLY)
            os.dup2(devnull, sys.stdout.fileno())
            sys.exit(1)  # Python exits with error code 1 on EPIPE

    if __name__ == '__main__':
        main()

  Do not set SIGPIPE’s disposition to SIG_DFL in order to avoid
  BrokenPipeError. Doing that would cause your program to exit
  unexpectedly whenever any socket connection is interrupted while
  your program is still writing to it.
  """

Currently, tools/perf/scripts/python/intel-pt-events.py seems to be the
only script that fixes the issue that way.

tools/perf/scripts/python/compaction-times.py uses another approach
signal.signal(signal.SIGPIPE, signal.SIG_DFL) but the Python
documentation clearly says "Don't do it".

I cannot fix all Python scripts since there are so many.
I fixed some in the scripts/ directory.

[1]: https://lore.kernel.org/all/202211161056.1B9611A@keescook/
[2]: https://github.com/llvm/llvm-project/issues/59037
[3]: 4787efa380
[4]: https://docs.python.org/3/library/signal.html#note-on-sigpipe

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>

2023-01-26 12:43:33 +09:00

gen_compile_commands.py kbuild: rename cmd_$@ to savedcmd_$@ in *.cmd files 2023-01-22 23:43:33 +09:00

run-clang-tools.py scripts: handle BrokenPipeError for python scripts 2023-01-26 12:43:33 +09:00