On Sat, Oct 30, 2010 at 10:14:23PM +0900, Tetsuo Handa wrote: > Sergey Senozhatsky wrote: > > On (10/29/10 13:16), Paul E. McKenney wrote: > > > Interesting... > > > > > > The task-list lock is read-held at this point, which should mean that > > > the PID mapping cannot change. The lockdep_tasklist_lock_is_held() > > > function does lockdep_is_held(&tasklist_lock), which must therefore > > > only be checking for write-holding the lock. The fix would be to > > > make lockdep_tasklist_lock_is_held() check for either read-holding or > > > write-holding tasklist lock. > > > > > > Or is there some subtle reason that read-holding the tasklist lock is > > > not sufficient? > > This was discussed in the thread at http://kerneltrap.org/mailarchive/linux-kernel/2009/12/10/4517520 . > Quoting from one of posts in that thead http://kerneltrap.org/mailarchive/linux-kernel/2010/2/8/4536388 > > | Usually tasklist gives enough protection, but if copy_process() fails > | it calls free_pid() lockless and does call_rcu(delayed_put_pid(). > | This means, without rcu lock find_pid_ns() can't scan the hash table > | safely. > > And now the patch that adds > > rcu_lockdep_assert(rcu_read_lock_held()); > > was merged in accordance with that comment. > Therefore, I thing below change is not good. > > > Should it be changed to (let's say) > > > > struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns) > > { > > - rcu_lockdep_assert(rcu_read_lock_held()); > > + rcu_lockdep_assert(rcu_read_lock_held() || lockdep_tasklist_lock_is_held()); > > return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID); > > } So we should remove the lockdep_tasklist_lock_is_held() and then apply Sergey's patch, correct? Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
