lkml.org 
[lkml]   [2010]   [Nov]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] posix-cpu-timers: rcu_read_lock/unlock protect find_task_by_vpid call
Just added Oleg to the cc-list

On Tue, 2 Nov 2010, Sergey Senozhatsky wrote:

> On (11/02/10 16:31), Thomas Gleixner wrote:
> > 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.
> >
>
> Please kindly review.
>
> ---
>
> diff --git a/kernel/posix-cpu-timers.c b/kernel/posix-cpu-timers.c
> index 6842eeb..96fe2a3 100644
> --- a/kernel/posix-cpu-timers.c
> +++ b/kernel/posix-cpu-timers.c
> @@ -37,13 +37,13 @@ static int check_clock(const clockid_t which_clock)
> if (pid == 0)
> 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;
> }
> - read_unlock(&tasklist_lock);
> + rcu_read_unlock();
>
> return error;
> }
> @@ -390,7 +390,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
>
> INIT_LIST_HEAD(&new_timer->it.cpu.entry);
>
> - read_lock(&tasklist_lock);
> + rcu_read_lock();
> if (CPUCLOCK_PERTHREAD(new_timer->it_clock)) {
> if (pid == 0) {
> p = current;
> @@ -414,7 +414,7 @@ int posix_cpu_timer_create(struct k_itimer *new_timer)
> } else {
> ret = -EINVAL;
> }
> - read_unlock(&tasklist_lock);
> + rcu_read_unlock();
>
> return ret;
> }
>
>


\
 
 \ /
  Last update: 2010-11-02 17:07    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site