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[llvm-exegesis] Kill process that recieve a signal #86069

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Merged
merged 1 commit into from
Mar 22, 2024
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[llvm-exegesis] Kill process that recieve a signal #86069

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18 changes: 16 additions & 2 deletions llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -342,7 +342,7 @@ class SubProcessFunctionExecutorImpl
return make_error<Failure>("Failed to attach to the child process: " +
Twine(strerror(errno)));

if (wait(NULL) == -1) {
if (waitpid(ParentOrChildPID, NULL, 0) == -1) {
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At that point ParentOrChildPID is always the parent, but it's not immediately obvious (I had to scroll up). What about restructuring this function to have:


[[noreturn]] void runChildSubprocess(int ReadFD, int FriteFD) {
   // We are in the child process, close the write end of the pipe.
      close(PipeFiles[1]);
      // Unregister handlers, signal handling is now handled through ptrace in
      // the host process.
      sys::unregisterHandlers();
      prepareAndRunBenchmark(PipeFiles[0], Key);
      llvm_unreachable("Child process didn't exit when expected.");
}

Error runParentSubprocess(pid_t PID, int ReadFD, int FriteFD) {
    const ExegesisTarget &ET = State.getExegesisTarget();
    ...
}


createSubProcessAndRunBenchmark() {
  ...
  if (ParentOrChildPID == -1) {
    ...
  }
  
  if (ParentOrChildPID == 0) {
     runChildSubprocess(PipeFiles[0], Pipefiles[1]);
      llvm_unreachable("Child process didn't exit when expected.");
  }

  return runParentSubprocess(ParentOrChildPID, PipeFiles[0], Pipefiles[1]);
}

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That's a good point. The suggested refactoring would definitely make the code cleaner. I'm going to land this PR and then open up another PR with the suggested refactoring to try and keep the history cleanish. Thanks for the suggestion!

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See #86232.

return make_error<Failure>(
"Failed to wait for child process to stop after attaching: " +
Twine(strerror(errno)));
Expand All @@ -361,7 +361,7 @@ class SubProcessFunctionExecutorImpl
return SendError;

int ChildStatus;
if (wait(&ChildStatus) == -1) {
if (waitpid(ParentOrChildPID, &ChildStatus, 0) == -1) {
return make_error<Failure>(
"Waiting for the child process to complete failed: " +
Twine(strerror(errno)));
Expand Down Expand Up @@ -401,6 +401,20 @@ class SubProcessFunctionExecutorImpl
Twine(strerror(errno)));
}

// Send SIGKILL rather than SIGTERM as the child process has no SIGTERM
// handlers to run, and calling SIGTERM would mean that ptrace will force
// it to block in the signal-delivery-stop for the SIGSEGV/other signals,
// and upon exit.
if (kill(ParentOrChildPID, SIGKILL) == -1)
return make_error<Failure>("Failed to kill child benchmarking proces: " +
Twine(strerror(errno)));

// Wait for the process to exit so that there are no zombie processes left
// around.
if (waitpid(ParentOrChildPID, NULL, 0) == -1)
return make_error<Failure>("Failed to wait for process to die: " +
Twine(strerror(errno)));

if (ChildSignalInfo.si_signo == SIGSEGV)
return make_error<SnippetSegmentationFault>(
reinterpret_cast<intptr_t>(ChildSignalInfo.si_addr));
Expand Down