Linus Torvalds <[EMAIL PROTECTED]> writes: > On Fri, 6 Apr 2007, Oleg Nesterov wrote: >> >> Oops. I misread stop_machine(), it does kernel_thread(), not >> kthread_create(). >> So "stopmachine" threads are all re-parented to init when the caller exits. >> I think it makes sense to set ->exit_state = -1 in stopmachine(), regadless >> of any other changes. > > I agree that "->exit_state = -1" makes sense, but I disagree in that I > don't think it *matters*. > > Most of the problematic kernel threads are long-running (as in "never > exit"). Things like eventd, khelper, migration-threads etc will have init > as their parent and never actually exit, so their ->exit_state doesn't > matter. What matters is that they are on the children list, so when you > have 1024 CPU's, and init has many thousand of these per-cpu threads as > its children, then the *user* threads (that do exit) will cause problems! > > I'd almost prefer to just not add kernel threads to any parent process > list *at*all*.
Oleg is coming from a different case where it was found that exiting kernel threads were causing problems for nash when nash was run as init in an initramfs. While I think that case is likely a user space bug because nash should check the pid from waidpid before assuming the process it was waiting for returned. I do think you can construct valid embedded cases where you can prove there that among the user space processes certain actions are safe when they exit that a spare kernel space thread could invalidate. It just happens that the exit signal of kernel threads just matters on the other end of system size. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/