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From:   Zqiang <qiang1.zhang@intel.com>
To:     paulmck@kernel.org, frederic@kernel.org
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH] rcu/nocb: Clear rdp offloaded flags when rcuop/rcuog kthreads spawn failed
Date:   Mon, 28 Feb 2022 17:36:29 +0800
Message-Id: <20220228093629.3746473-1-qiang1.zhang@intel.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
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When CONFIG_RCU_NOCB_CPU is enabled and 'rcu_nocbs' is set, the rcuop
and rcuog kthreads is created. however the rcuop or rcuog kthreads
creation may fail, if failed, clear rdp offloaded flags.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
 kernel/rcu/tree_nocb.h | 14 ++++++++++++--
 1 file changed, 12 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_nocb.h b/kernel/rcu/tree_nocb.h
index 46694e13398a..94b279147954 100644
--- a/kernel/rcu/tree_nocb.h
+++ b/kernel/rcu/tree_nocb.h
@@ -1246,7 +1246,7 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 				"rcuog/%d", rdp_gp->cpu);
 		if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo GP kthread, OOM is now expected behavior\n", __func__)) {
 			mutex_unlock(&rdp_gp->nocb_gp_kthread_mutex);
-			return;
+			goto end;
 		}
 		WRITE_ONCE(rdp_gp->nocb_gp_kthread, t);
 		if (kthread_prio)
@@ -1258,12 +1258,22 @@ static void rcu_spawn_cpu_nocb_kthread(int cpu)
 	t = kthread_run(rcu_nocb_cb_kthread, rdp,
 			"rcuo%c/%d", rcu_state.abbr, cpu);
 	if (WARN_ONCE(IS_ERR(t), "%s: Could not start rcuo CB kthread, OOM is now expected behavior\n", __func__))
-		return;
+		goto end;
 
 	if (kthread_prio)
 		sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
 	WRITE_ONCE(rdp->nocb_cb_kthread, t);
 	WRITE_ONCE(rdp->nocb_gp_kthread, rdp_gp->nocb_gp_kthread);
+	return;
+end:
+	if (cpumask_test_cpu(cpu, rcu_nocb_mask)) {
+		rcu_segcblist_offload(&rdp->cblist, false);
+		rcu_segcblist_clear_flags(&rdp->cblist,
+				SEGCBLIST_KTHREAD_CB | SEGCBLIST_KTHREAD_GP);
+		rcu_segcblist_clear_flags(&rdp->cblist, SEGCBLIST_LOCKING);
+		rcu_segcblist_set_flags(&rdp->cblist, SEGCBLIST_RCU_CORE);
+	}
+	return;
 }
 
 /* How many CB CPU IDs per GP kthread?  Default of -1 for sqrt(nr_cpu_ids). */
-- 
2.25.1