Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 2 Nov 2010 16:31:37 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call |
| |
On Tue, 2 Nov 2010, Sergey Senozhatsky wrote:
> Commit 4221a9918e38b7494cee341dda7b7b4bb8c04bde "Add RCU check for > find_task_by_vpid()" introduced rcu_lockdep_assert to find_task_by_pid_ns. > Add rcu_read_lock/rcu_read_unlock to call find_task_by_vpid. > > Tetsuo Handa wrote: > > 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.
We can remove the tasklist_lock while at it. rcu_read_lock is enough.
Thanks,
tglx
> > Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com> > > --- > > diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c > index 6842eeb..855bc53 100644 > --- a/kernel/posix-cpu-timers.c > +++ b/kernel/posix-cpu-timers.c > @@ -38,11 +38,13 @@ static int check_clock(const clockid_t which_clock) > return 0; > > read_lock(&tasklist_lock); > + rcu_read_lock(); > p = find_task_by_vpid(pid); > if (!p || !(CPUCLOCK_PERTHREAD(which_clock) ? > same_thread_group(p, current) : thread_group_leader(p))) { > error = -EINVAL; > } > + rcu_read_unlock(); > read_unlock(&tasklist_lock); > > return error; > @@ -395,17 +397,21 @@ int posix_cpu_timer_create(struct k_itimer *new_timer) > if (pid == 0) { > p = current; > } else { > + rcu_read_lock(); > p = find_task_by_vpid(pid); > if (p && !same_thread_group(p, current)) > p = NULL; > + rcu_read_unlock(); > } > } else { > if (pid == 0) { > p = current->group_leader; > } else { > + rcu_read_lock(); > p = find_task_by_vpid(pid); > if (p && !thread_group_leader(p)) > p = NULL; > + rcu_read_unlock(); > } > } > new_timer->it.cpu.task = p; >
| ![\](/images/icornerr.gif) |