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    SubjectRe: [PATCH 04/23] vfs: Introduce infrastructure for revoking a file
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    Hi Eric,

    On Tue, Jun 2, 2009 at 12:50 AM, Eric W. Biederman
    <ebiederm@xmission.com> wrote:
    > +#ifdef CONFIG_FILE_HOTPLUG
    > +
    > +static bool file_in_use(struct file *file)
    > +{
    > +       struct task_struct *leader, *task;
    > +       bool in_use = false;
    > +       int i;
    > +
    > +       rcu_read_lock();
    > +       do_each_thread(leader, task) {
    > +               for (i = 0; i < MAX_FILE_HOTPLUG_LOCK_DEPTH; i++) {
    > +                       if (task->file_hotplug_lock[i] == file) {
    > +                               in_use = true;
    > +                               goto found;
    > +                       }
    > +               }
    > +       } while_each_thread(leader, task);
    > +found:
    > +       rcu_read_unlock();
    > +       return in_use;
    > +}

    This seems rather heavy-weight. If we're going to use this
    infrastructure for forced unmount, I think this will be a problem.

    Can't we two this in two stages: (1) mark a bit that forces
    file_hotplug_read_trylock to always fail and (2) block until the last
    remaining in-kernel file_hotplug_read_unlock() has executed?

    Pekka
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