On Wed, 8 Feb 2023, Shaopeng Tan (Fujitsu) wrote:
> > On Tue, 31 Jan 2023, Shaopeng Tan wrote:
> >
> > > After creating a child process with fork() in CAT test, if an error
> > > occurs or a signal such as SIGINT is received, the parent process will
> > > be terminated immediately, and therefor the child process will not be
> > > killed and also resctrlfs is not unmounted.
> > >
> > > There is a signal handler registered in CMT/MBM/MBA tests, which kills
> > > child process, unmount resctrlfs, cleanups result files, etc., if a
> > > signal such as SIGINT is received.
> > >
> > > Commonize the signal handler registered for CMT/MBM/MBA tests and
> > > reuse it in CAT too.
> > >
> > > To reuse the signal handler, make the child process in CAT wait to be
> > > killed by parent process in any case (an error occurred or a signal
> > > was received), and when killing child process use global bm_pid
> > > instead of local bm_pid.
> > >
> > > Also, since the MBA/MBA/CMT/CAT are run in order, unregister the
> > > signal handler at the end of each test so that the signal handler
> > > cannot be inherited by other tests.
> > >
> > > Signed-off-by: Shaopeng Tan <tan.shaopeng@xxxxxxxxxxxxxx>
> > > ---
> >
> > > if (bm_pid == 0) {
> > > /* Tell parent that child is ready */
> > > close(pipefd[0]);
> > > pipe_message = 1;
> > > if (write(pipefd[1], &pipe_message, sizeof(pipe_message)) <
> > > - sizeof(pipe_message)) {
> > > - close(pipefd[1]);
> > > + sizeof(pipe_message))
> > > + /*
> > > + * Just print the error message.
> > > + * Let while(1) run and wait for itself to be killed.
> > > + */
> > > perror("# failed signaling parent process");
> >
> > If the write error is ignored here, won't it just lead to parent hanging forever
> > waiting for the child to send the message through the pipe which will never
> > come?
>
> If the write error is ignored here, the pipe will be closed by "close(pipefd[1]);" and child process will wait to be killed by "while(1)".
> ---
> - return errno;
> - }
>
> close(pipefd[1]);
> while (1)
> ---
>
> If all file descriptors referring to the write end of a pipe have been closed,
> then an attempt to read(2) from the pipe will see end-of-file (read(2) will return 0).
> Then, "perror("# failed reading from child process");" occurs.
> ---
> } else {
> /* Parent waits for child to be ready. */
> close(pipefd[1]);
> pipe_message = 0;
> while (pipe_message != 1) {
> if (read(pipefd[0], &pipe_message,
> sizeof(pipe_message)) < sizeof(pipe_message)) {
> perror("# failed reading from child process");
> break;
> }
> }
> close(pipefd[0]);
> kill(bm_pid, SIGKILL);
> signal_handler_unregister();
> }
Ah, indeed read() will pick up the close event. So your code seem fine
after all.
--
i.
