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    SubjectRe: [PATCH] Add module_kernel_thread for threads that live in modules.
    In message <16110.20088.351260.156860@gargle.gargle.HOWL> you write:
    > On Monday June 16, wrote:
    > > Hi Neil,
    > Hi Rusty. Thanks for the comments... I probably should have Cc:ed you
    > in the first place....

    Yeah, that does tend to get faster response, but I know some hackers
    consider it completely optional 8(

    > > There are several problems with this patch. Ignoring the fact
    > > that you use __module_get. Firstly, you bump the module count
    > > permentantly while the thread is running: how does it ever get
    > > unloaded? Secondly, modprobe becomes your parent.
    > We seem to have very different views of the problem, as you seem to be
    > calling into question aspects that I thought were obviously correct.
    > __module_get:
    > In all the cases I am interested in (nfsd, lockd,
    > lockd-helper-thread), the thread is started by code running
    > inside the module and so there will be a reference held on the
    > module while the thread is being started, thus __module_get is the
    > correct thing to do as "we know we already have a refcount"...

    But do you wait for it? Theoretically the init code could have
    finished, and someone done rmmod, before this thread gets as far as
    __module_get, no?

    > module count bumped permananelt while thread is running:
    > well ofcourse, the thread runs code in the module which can only
    > be done safely while we have a ref-count.

    For future reference: this isn't quite true. If a function/thread is
    synchronously stopped by the exit code/failed init code then they
    don't need to hold a reference count: it still *can* hold a reference
    count, which really depends on whether the module should be considered
    "in use" by the thread... cf. timers.

    > The threads I am thinking of aren't running "whenever the module is
    > loaded". They are running "whenever their service is needed".

    My bad: I wasn't sure given my (admittedly brief) glance at the code.
    Thanks for clarifing!

    > modprobe becomes your parent:
    > No, modprobe has nothing to do with it in my case. rpc.nfsd, or
    > mount_nfs or lockd might be the parent. I thought reparent_to_init
    > handled all that. Apparently there are question marks over that
    > which I wasn't aware of.

    Andrew has been trying to kill it, and I think he's right. In
    practical terms, it's much easier to start from a clean environment
    than to clean up an unknown one, and keep that cleanup code uptodate.

    > I don't want to have to call "cleanup_thread" or de-allocate the
    > "struct kthread". I want to be able to SIGKILL a process and have it
    > go away and release everything, including possibly the last refernce
    > to the module.
    > In short, it really feels like we are trying to solve different
    > problems :-)

    Agreed: threads under their own control are much simpler than ones
    under external control.

    > I will have a look at keventd and see if it's services can be of
    > assistance to solve my problem.

    I will think, which usually seems to help me when presented with new
    information 8)

    Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
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