On Mon, May 14, 2018 at 01:33:20PM -0700, Paul E. McKenney wrote: > On Sun, May 13, 2018 at 08:15:41PM -0700, Joel Fernandes (Google) wrote: > > cpustart shows a stale gp_seq. This is because rdp->gp_seq is updated > > only at the end of the __note_gp_changes function. For this reason, use > > rnp->gp_seq instead. I believe we can't update rdp->gp_seq too early so > > lets just use the gp_seq from rnp instead. > > > > Signed-off-by: Joel Fernandes (Google) <[email protected]> > > I took this one with the usual commit-log update. Please take a look!
Looks good, thanks! - Joel > > Thanx, Paul > > ------------------------------------------------------------------------ > > commit 3e14c6a5225d201776edd9a96d9c9b4435855446 > Author: Joel Fernandes (Google) <[email protected]> > Date: Sun May 13 20:15:41 2018 -0700 > > rcu: Fix cpustart tracepoint gp_seq number > > The "cpustart" trace event shows a stale gp_seq. This is because it uses > rdp->gp_seq, which is updated only at the end of the __note_gp_changes() > function. This commit therefore instead uses rnp->gp_seq. > > An alternative fix would be to update rdp->gp_seq earlier, but this would > break RCU's detection of the beginning of a new-to-this-CPU grace period. > > Signed-off-by: Joel Fernandes (Google) <[email protected]> > Signed-off-by: Paul E. McKenney <[email protected]> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index de6447dd73de..23b855f5c5cb 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -1796,7 +1796,7 @@ static bool __note_gp_changes(struct rcu_state *rsp, > struct rcu_node *rnp, > * set up to detect a quiescent state, otherwise don't > * go looking for one. > */ > - trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpustart")); > + trace_rcu_grace_period(rsp->name, rnp->gp_seq, TPS("cpustart")); > need_gp = !!(rnp->qsmask & rdp->grpmask); > rdp->cpu_no_qs.b.norm = need_gp; > rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr); >
