Messages in this thread Patch in this message | | | Date | Mon, 14 May 2018 13:33:20 -0700 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH RFC 8/8] rcu: Fix cpustart tracepoint gp_seq number |
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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) <joel@joelfernandes.org>
I took this one with the usual commit-log update. Please take a look!
Thanx, Paul
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commit 3e14c6a5225d201776edd9a96d9c9b4435855446 Author: Joel Fernandes (Google) <joel@joelfernandes.org> 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) <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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);
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