Re: [PATCH 5/6] IMA: use rbtree instead of radix tree for inodeinformation cache

[Linus Torvalds]

On Wed, Oct 20, 2010 at 3:05 PM, Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> /me wanders off to look at converting the xfs buffer cache rbtrees
> to RCU....

Look out for livelocks, though. And yes, they can happen.

So rather than a loop, one option is to do basically

  rcu_read_lock();
  seq = read_seqbegin();

  .. do lookup ..

  need_lock = read_seqretry(seq);
  rcu_read_unlock();

  if (need_lock) {
    get_real_lock();

    .. do lookup ..

    drop_real_lock();
 }

which just falls back to a locked access if the rcu model doesn't work.

                             Linus
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