On Sun, 14 Aug 2011 19:51:19 +0200 Oleg Nesterov <oleg@xxxxxxxxxx> 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 _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
