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From:   Zqiang <qiang1.zhang@intel.com>
To:     paulmck@kernel.org, frederic@kernel.org
Cc:     rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] rcu: Add cpu-exp indicator to expedited RCU CPU stall warnings
Date:   Wed, 18 May 2022 19:43:10 +0800
Message-Id: <20220518114310.1478091-1-qiang1.zhang@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

This commit adds a "D" indicator to expedited RCU CPU stall warnings.
when an expedited grace period begins, due to CPU disable interrupt
time too long, cause the IPI(rcu_exp_handler()) unable to respond in
time, this debugging id will be showed.

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

rcu_torture_stall start on CPU 1.
............
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>
---
 kernel/rcu/tree_exp.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 4c7037b50703..f092c7f18a5f 100644
--- 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",
-- 
2.25.1