lkml.org 
[lkml]   [2011]   [Aug]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: Possible race between cgroup_attach_proc and de_thread, and questionable code in de_thread.
    On Sun, 14 Aug 2011 19:51:19 +0200 Oleg Nesterov <oleg@redhat.com> wrote:

    > On 07/28, Paul E. McKenney wrote:
    > >
    > > On Thu, Jul 28, 2011 at 11:08:13AM +1000, NeilBrown wrote:
    > > >
    > > > I disagree. It also requires - by virtue of the use of while_each_thread() -
    > > > that 'g' remains on the list that 't' is walking along.
    > >
    > > Doesn't the following code in the loop body deal with this possibilty?
    > >
    > > /* Exit if t or g was unhashed during refresh. */
    > > if (t->state == TASK_DEAD || g->state == TASK_DEAD)
    > > goto unlock;
    >
    > This code is completely wrong even if while_each_thread() was fine.
    >
    > I sent the patch but it was ignored.
    >
    > [PATCH] fix the racy check_hung_uninterruptible_tasks()->rcu_lock_break()
    > http://marc.info/?l=linux-kernel&m=127688790019041
    >
    > Oleg.


    I agree with that patch.
    RCU only protects a task_struct until release_task() is called (which
    removes it from the task list).

    So holding rcu_lock doesn't stop put_task_struct from freeing the memory
    unless we *know* that release_task hasn't been called. This is exactly that
    pid_alive() tests.


    I must say that handling of task_struct seems to violate the law of least
    surprise a little to often for my taste. Maybe it is just a difficult
    problem and it needs a complex solution - but it would be really nice if it
    were a bit simpler :-(

    NeilBrown


    \
     
     \ /
      Last update: 2011-08-15 02:01    [W:0.019 / U:61.460 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site