linux-kernel - [PATCH AUTOSEL 5.4 1/2] rcu: Fix __this_cpu_read() lockdep warning in rcu_force_quiescent

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Message-Id: <20221217001116.41497-1-sashal@kernel.org>
Date:   Fri, 16 Dec 2022 19:11:14 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Zqiang <qiang1.zhang@...el.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Sasha Levin <sashal@...nel.org>, frederic@...nel.org,
        quic_neeraju@...cinc.com, josh@...htriplett.org,
        rcu@...r.kernel.org
Subject: [PATCH AUTOSEL 5.4 1/2] rcu: Fix __this_cpu_read() lockdep warning in rcu_force_quiescent_state()

From: Zqiang <qiang1.zhang@...el.com>

[ Upstream commit ceb1c8c9b8aa9199da46a0f29d2d5f08d9b44c15 ]

Running rcutorture with non-zero fqs_duration module parameter in a
kernel built with CONFIG_PREEMPTION=y results in the following splat:

BUG: using __this_cpu_read() in preemptible [00000000]
code: rcu_torture_fqs/398
caller is __this_cpu_preempt_check+0x13/0x20
CPU: 3 PID: 398 Comm: rcu_torture_fqs Not tainted 6.0.0-rc1-yoctodev-standard+
Call Trace:
<TASK>
dump_stack_lvl+0x5b/0x86
dump_stack+0x10/0x16
check_preemption_disabled+0xe5/0xf0
__this_cpu_preempt_check+0x13/0x20
rcu_force_quiescent_state.part.0+0x1c/0x170
rcu_force_quiescent_state+0x1e/0x30
rcu_torture_fqs+0xca/0x160
? rcu_torture_boost+0x430/0x430
kthread+0x192/0x1d0
? kthread_complete_and_exit+0x30/0x30
ret_from_fork+0x22/0x30
</TASK>

The problem is that rcu_force_quiescent_state() uses __this_cpu_read()
in preemptible code instead of the proper raw_cpu_read().  This commit
therefore changes __this_cpu_read() to raw_cpu_read().

Signed-off-by: Zqiang <qiang1.zhang@...el.com>
Reviewed-by: Joel Fernandes (Google) <joel@...lfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 5797cf2909b0..615283404d9d 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -2317,7 +2317,7 @@ void rcu_force_quiescent_state(void)
 	struct rcu_node *rnp_old = NULL;

 	/* Funnel through hierarchy to reduce memory contention. */
-	rnp = __this_cpu_read(rcu_data.mynode);
+	rnp = raw_cpu_read(rcu_data.mynode);
 	for (; rnp != NULL; rnp = rnp->parent) {
 		ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
 		      !raw_spin_trylock(&rnp->fqslock);
-- 
2.35.1