Re: [patch 1/9] sys: Fix missing rcu protection for __task_cred()access

Thomas Gleixner
2009-12-10T21:17:53Z

On Fri, 11 Dec 2009, Tetsuo Handa wrote:
> > 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.
>
> So, we need to change below comment from "or" to "and" ?

No, both functions must be called with rcu_read_lock()

tasklist_lock read-held is not protecting the rcu lists and does not
protect against a concurrent update. It merily protects against tasks
going away or being added while we look up the lists.

> 378 /*
> 379 * Must be called under rcu_read_lock() or with tasklist_lock read-held.
> 380 */
> 381 struct task_struct *find_task_by_pid_ns(pid_t nr, struct pid_namespace *ns)
> 382 {
> 383 return pid_task(find_pid_ns(nr, ns), PIDTYPE_PID);
> 384 }
> 385
> 386 struct task_struct *find_task_by_vpid(pid_t vnr)
> 387 {
> 388 return find_task_by_pid_ns(vnr, current->nsproxy->pid_ns);
> 389 }
>

Thanks,

tglx