lkml.org 
[lkml]   [2007]   [Sep]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 1/4] module: implement module_inhibit_unload()
    On Tue, 25 Sep 2007, Tejun Heo wrote:

    > Jonathan Corbet wrote:
    > > Hi, Tejun,
    > >
    > > I was just looking over these changes...
    > >
    > >> + /* Don't proceed till inhibition is lifted. */
    > >> + add_wait_queue(&module_unload_wait, &wait);
    > >> + set_current_state(TASK_UNINTERRUPTIBLE);
    > >> + if (atomic_read(&module_unload_inhibit_cnt))
    > >> + schedule();
    > >> + __set_current_state(TASK_RUNNING);
    > >> + remove_wait_queue(&module_unload_wait, &wait);
    > >> +
    > >> + mutex_lock(&module_mutex);
    > >
    > > Maybe I'm missing something, but this looks racy to me. There's no
    > > check after schedule() to see if module_unload_inhibit_cnt is really
    > > zero, and nothing to keep somebody else from slipping in and raising it
    > > again afterward.
    >
    > The unloading can proceed once module_unload_inhibit_cnt reaches zero.
    > An unloading thread only has to care about inhibition put in effect
    > before unloading has started, so there's no need to check again.

    You haven't fully answered Jon's question. Suppose
    module_unload_inhibit_cnt is nonzero, so the task adds itself to the
    module_unload_wait queue, changes to TASK_UNINTERRUPTIBLE, and calls
    schedule. There's nothing to prevent somebody else from waking the
    task back up before the original inhibition has been lifted.

    Alan Stern

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-09-25 16:27    [W:0.034 / U:0.164 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site