On Wed, Jun 11, 2014 at 12:23:57AM -0400, Pranith Kumar wrote: > Hi Paul, > > On Wed, Jun 11, 2014 at 12:12 AM, Paul E. McKenney > <paul...@linux.vnet.ibm.com> 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 :)
Hmmm... Now that you mention it, that does look a bit strange. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/