tasklist_lock question

[Chris Moller]

Roland McGrath wrote:
>> y'all might get multiple copies of this--i think the stuttgart smtp
>> server i've been using might not be working right...
>>     
>
> I got two copies, but one of them stole an R from you!
>
>   
>> looks like stuff that used to be wrapped up in
>> rcu_read_lock()/rcu_read_unlock() is now wrapped up in
>> read_lock(&tasklist_lock)/read_unlock(&tasklist_lock) but tasklist_lock
>> is showing up as undefined in module build stage 2 and "Unknown symbol
>> in module" in insmod.  am i balling something up?  or can i go on using
>> rcu_read_(un)?lock?
>>     
>
> In the new utrace API there is nothing that requires you to use either RCU
> or tasklist_lock.  If you are using RCU for your own purposes, that's up to
> you.  The tasklist_lock has not been exported for modules to use in a long
> time.  Please be specific in your questions.  What are you doing that you
> think needs some locking you aren't doing?
>   

A little fnc to get the task associated with a given pid:

    static struct task_struct *
    get_task (long utraced_pid)
    {
      struct task_struct * task;

      read_lock (&tasklist_lock);
      task = find_task_by_vpid(utraced_pid);
      if (task) get_task_struct(task);
      read_unlock (&tasklist_lock);

      return task;
    }


I know you've got utrace_attach_pid(), but there are other circumstances
I've used in the past, like accessing user mem via get_user_pages(),
where I needed access to the task struct.  Even if I don't need task
struct any more for utrace, I'm kinda trying to plan ahead a bit.

Or are pid_task() and get_pid_task() the new/modern way of doing that
w/o needing your own locking?

cm

>
> Thanks,
> Roland
>   

-- 
Chris Moller

  I know that you believe you understand what you think I said, but
  I'm not sure you realize that what you heard is not what I meant.
      -- Robert McCloskey


-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 251 bytes
Desc: OpenPGP digital signature
URL: <http://listman.redhat.com/archives/utrace-devel/attachments/20080903/769e6f65/attachment.sig>