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    SubjectRe: [PATCH 2/3] Keys: Use RCU to manage session keyring pointer
    On Tue, Apr 12, 2005 at 10:11:50AM +0100, David Howells wrote:
    > Paul E. McKenney <paulmck@us.ibm.com> wrote:
    >
    > > > spin_lock_irqsave(&tsk->sighand->siglock, flags);
    > > > - old = tsk->signal->session_keyring;
    > > > - tsk->signal->session_keyring = keyring;
    > > > + old = rcu_dereference(tsk->signal->session_keyring);
    > >
    > > I don't understand why rcu_dereference() is needed in this case.
    > > Since we are holding the lock, it should not be possible for
    > > this to change, right? Or am I missing something? (Quite possible,
    > > am not all that familiar with this code.)
    >
    > Erm... you're right. I stuck the rcu_dereference() in then added the locks
    > back in when I realised I still needed them.
    >
    > > > + synchronize_kernel();
    > >
    > > This would want to become synchronize_rcu().
    >
    > I think the deprecation happened since I wrote my patch.

    Yes, sorry, I should have made it clear that this was a change that
    affected your code rather than an error on your part.

    > > > + if (tsk->signal->session_keyring) {
    > > > + rcu_read_lock();
    > > > + key = keyring_search_aux(
    > > > + rcu_dereference(tsk->signal->session_keyring),
    > > > + type, description, match);
    > > > + rcu_read_unlock();
    > > > + }
    > > > + else {
    > > > + key = keyring_search_aux(tsk->user->session_keyring,
    > > > + type, description, match);
    > >
    > > This one is constant, right? If not, I don't understand the locking design.
    >
    > Which one? tsk->user->session_keyring is, tsk->signal->session_keyring is not.

    Good, that matches the code!

    Thanx, Paul

    > Thanks for the review.
    >
    > David
    >
    -
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