rcu: Avoid spurious RCU CPU stall warnings

If a given CPU avoids the idle loop but also avoids starting a new
RCU grace period for a full minute, RCU can issue spurious RCU CPU
stall warnings.  This commit fixes this issue by adding a check for
ongoing grace period to avoid these spurious stall warnings.

Reported-by: Becky Bruce <bgillbruce@gmail.com>
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

1 files changed, 2 insertions, 1 deletions

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 2cf8eb3e2d43..98f275296c6d 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -819,7 +819,8 @@ static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
         j = ACCESS_ONCE(jiffies);
         js = ACCESS_ONCE(rsp->jiffies_stall);
         rnp = rdp->mynode;
-        if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
+        if (rcu_gp_in_progress(rsp) &&
+            (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
 
                 /* We haven't checked in, so go dump stack. */
                 print_cpu_stall(rsp);