Description:
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If PHP is started in FastCGI mode managing several child workers, and the SIGCHLD handler is inherited as SIG_IGN from the parent process, the wait() loop doesn't work as intended, since wait() does not report auto-reaped children.

Instead, it will start looping indefinitely once all children have exited, since wait() will start returning ECHILD before exit_signal has been set, eating CPU until killed.

Inheriting SIGCHLD as SIG_IGN may arguably be a rare condition, but it probably doesn't hurt to reset it to SIG_DFL, since PHP does depend on it for proper behavior.