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    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;
    > }
    >
    >


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