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); > } Regards. -- 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
