Hi Paul, On Wed, Jun 11, 2014 at 12:12 AM, Paul E. McKenney <[email protected]> wrote: >> if (rnp->gpnum != rnp->completed || >> - ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) { >> + ACCESS_ONCE(rnp_root->gpnum) != ACCESS_ONCE(rnp_root->completed)) { > > At this point in the code, we are checking the current rcu_node structure, > which might or might not be the root. If it is not the root, we absolutely > cannot compare against the root because we don't yet hold the root's lock. >
I was a bit thrown by the double checking which is being done (rnp->gpnum != rnp->complete) in that if condition. Once without ACCESS_ONCE and one with. Is there any particular reason for this? I now understand that we are comparing ->gpnum and ->completed of the root node which might change from under us if we don't hold the root's lock. I will keep looking :) Thanks! -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
