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    Subject[PATCH tip/core/rcu 34/40] rcu: Fix cpustart tracepoint gp_seq number
    Date
    From: "Joel Fernandes (Google)" <joel@joelfernandes.org>

    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>
    ---
    kernel/rcu/tree.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
    index 8dab564be8e7..5c6f59b4fc9c 100644
    --- a/kernel/rcu/tree.c
    +++ b/kernel/rcu/tree.c
    @@ -1801,7 +1801,7 @@ 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);
    --
    2.17.1
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