I wonder if anybody uses kdb_stop_cpus with non-default value. If, yes, I am very interested to learn about your usecase for it.
I think that the default kdb behavior is the correct one, so it doesn't make sense to have a knob to turn on incorrect behavior. But I may be missing something obvious. The comment in the code doesn't really satisfy me: /* * Flag indicating whether or not to IPI the other CPUs to stop them on * entering the debugger. Sometimes, this will result in a deadlock as * stop_cpus() waits for the other cpus to stop, so we allow it to be * disabled. In order to maximize the chances of success, use a hard * stop for that. */ The hard stop should be sufficiently mighty. Yes, I am aware of supposedly extremely rare situations where a deadlock could happen even when using hard stop. But I'd rather fix that than have this switch. Oh, the commit message (from 2004) explains it: > Add a new sysctl, debug.kdb.stop_cpus, which controls whether or not we > attempt to IPI other cpus when entering the debugger in order to stop > them while in the debugger. The default remains to issue the stop; > however, that can result in a hang if another cpu has interrupts disabled > and is spinning, since the IPI won't be received and the KDB will wait > indefinitely. We probably need to add a timeout, but this is a useful > stopgap in the mean time. But that was before we started using hard stop in this context (in 2009). -- Andriy Gapon _______________________________________________ freebsd-current@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-current To unsubscribe, send any mail to "freebsd-current-unsubscr...@freebsd.org"
