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    SubjectRe: [PATCH] kthread: Don't depend on work queues
    On Wednesday, 11 April 2007 09:03, Andrew Morton wrote:
    > On Tue, 10 Apr 2007 23:44:36 -0600 (Eric W. Biederman) wrote:
    > > Currently there is a circular reference between work queue initialization
    > > and kthread initialization. This prevents the kernel thread
    > > infrastructure from initializing until after work queues have been
    > > initialized.
    > >
    > > For kernel threads we want something that is as close as possible to the
    > > init_task and is not contaminated by user processes. The later we start
    > > our kthreadd that forks the rest of the kernel threads the harder this is
    > > to do and the more of a mess we have to clean up because the defaults have
    > > changed on us.
    > >
    > > So this patch modifies the kthread support to not use work queues but to
    > > instead use a simple list of structures, and to have kthreadd start from
    > > init_task immediately after our kernel thread that execs /sbin/init.
    > >
    > > By being a true child of init_task we only have to change those process
    > > settings that we want to have different from init_task, such as our
    > > process name, blocking all signals and setting SIGCHLD to SIG_IGN
    > > so that all of our children are reaped automatically.
    > >
    > > By being a tre child of init_task we also naturally get our ppid set to 0
    > > and do not wind up as a child of PID == 1. Ensuring that kernel threads
    > > will not slow down the functioning of the wait family of functions.
    > argh. Your description freely confuddles the terms "kernel thread" and
    > "kthread". Can we not do that? Henceforth the term "kernel thread" refers
    > to something which was started with kernel_thread() and "kthread" refers to
    > something which was created by kthread_create(), OK?
    > Your patch gets midly tangled up with Oleg's recent
    > reduce-reparent_to_init.patch
    > make-kernel-threads-invisible-to-sbin-init.patch
    > reparent-kernel-threads-to-swapper.patch
    > but they seemed fairly unpopular anyway so I'll drop 'em.
    > Your wait_event() will contribute to load average, I expect. We get mail.
    > I converted it to wait_event_interruptible().
    > I guess using PF_NOFREEZE rather than try_to_freeze() is OK, but one
    > wonders what thinking led to that?

    It should be calling try_to_freeze() somewhere anyway. We may need to freeze
    all tasks in some cases.

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