rcu: Add irqs-disabled indicator to expedited RCU CPU stall warnings

If a CPU has interrupts disabled continuously starting before the
beginning of a given expedited RCU grace period, that CPU will not
execute that grace period's IPI handler.  This will in turn mean
that the ->cpu_no_qs.b.exp field in that CPU's rcu_data structure
will continue to contain the boolean value false.

Knowing whether or not a CPU has had interrupts disabled can be helpful
when debugging an expedited RCU CPU stall warning, so this commit
adds a "D" indicator expedited RCU CPU stall warnings that signifies
that the corresponding CPU has had interrupts disabled throughout.

This capability was tested as follows:

runqemu kvm slirp nographic qemuparams="-m 4096 -smp 4"  bootparams=
"isolcpus=2,3 nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1
rcutorture.stall_cpu_holdoff=30 rcutorture.stall_cpu=40
rcutorture.stall_cpu_irqsoff=1 rcutorture.stall_cpu_block=0
rcutorture.stall_no_softlockup=1" -d

The rcu_torture_stall() function ran on CPU 1, which displays the "D"
as expected given the rcutorture.stall_cpu_irqsoff=1 module parameter:

............
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks:
{ 1-...D } 26467 jiffies s: 13317 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug): l=1:0-1:0x2/.
Task dump for CPU 1:
task:rcu_torture_sta state:R  running task     stack:    0 pid:   76  ppid:     2 flags:0x00004008

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 4c7037b..f092c7f 100644 (file)
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -637,10 +637,11 @@ static void synchronize_rcu_expedited_wait(void)
                                        continue;
                                ndetected++;
                                rdp = per_cpu_ptr(&rcu_data, cpu);
-                               pr_cont(" %d-%c%c%c", cpu,
+                               pr_cont(" %d-%c%c%c%c", cpu,
                                        "O."[!!cpu_online(cpu)],
                                        "o."[!!(rdp->grpmask & rnp->expmaskinit)],
-                                       "N."[!!(rdp->grpmask & rnp->expmaskinitnext)]);
+                                       "N."[!!(rdp->grpmask & rnp->expmaskinitnext)],
+                                       "D."[!!(rdp->cpu_no_qs.b.exp)]);
                        }
                }
                pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n",