linux-kernel - [PATCH] rcu/nocb: Fix using smp_processor

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Date: Thu,  9 May 2024 15:40:46 +0800
From: Zqiang <qiang.zhang1211@...il.com>
To: paulmck@...nel.org,
	frederic@...nel.org,
	neeraj.upadhyay@...nel.org,
	joel@...lfernandes.org
Cc: qiang.zhang1211@...il.com,
	rcu@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] rcu/nocb: Fix using smp_processor_id() in preemptible warning

Currently, the this_cpu_ptr(&rcu_data) in rcu_rdp_is_offloaded() is called
before the condition "!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())"
is checked, and occurs in preemptible task context, this will trigger the
following warning.

[ 4.106221][ T18] BUG: using smp_processor_id() in preemptible [00000000] code: rcuop/0/18
[ 4.107796][ T18] caller is debug_smp_processor_id (lib/smp_processor_id.c:61)
[ 4.108547][ T18] CPU: 0 PID: 18 Comm: rcuop/0 Not tainted 6.9.0-rc2-00079-g4c66bc7cacc0 #1
[ 4.109667][ T18] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
[ 4.111064][ T18] Call Trace:
[ 4.111064][ T18]  <TASK>
[ 4.111064][ T18] dump_stack_lvl (lib/dump_stack.c:116)
[ 4.111064][ T18] dump_stack (lib/dump_stack.c:124)
[ 4.111064][ T18] check_preemption_disabled (arch/x86/include/asm/preempt.h:84 (discriminator 15) lib/smp_processor_id.c:53 (discriminator 15))
[ 4.111064][ T18] debug_smp_processor_id (lib/smp_processor_id.c:61)
[ 4.111064][ T18] rcu_rdp_is_offloaded (kernel/rcu/tree_plugin.h:27 (discriminator 1))
[ 4.111064][ T18] nocb_cb_wait (kernel/rcu/tree_nocb.h:936 (discriminator 2))
[ 4.111064][ T18] rcu_nocb_cb_kthread (kernel/rcu/tree_nocb.h:983 (discriminator 1))
[ 4.111064][ T18] ? nocb_cb_wait (kernel/rcu/tree_nocb.h:976)
[ 4.111064][ T18] kthread (kernel/kthread.c:388)
[ 4.111064][ T18] ? kthread (kernel/kthread.c:373 (discriminator 2))
[ 4.111064][ T18] ? kthread_complete_and_exit (kernel/kthread.c:341)
[ 4.111064][ T18] ret_from_fork (arch/x86/kernel/process.c:153)
[ 4.111064][ T18] ? kthread_complete_and_exit (kernel/kthread.c:341)
[ 4.111064][ T18] ret_from_fork_asm (arch/x86/entry/entry_64.S:256)
[ 4.111064][ T18]  </TASK>

This commit fix this warning by priority check the condition 
"!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())" , to
ensure whether the this_cpu_ptr(&rcu_data) can be executed in
rcu_rdp_is_offloaded().

Fixes: 8feeeba60711 ("rcu/nocb: Use kthread parking instead of ad-hoc implementation")
Tested-by: kernel test robot <oliver.sang@...el.com>
Signed-off-by: Zqiang <qiang.zhang1211@...il.com>
---
 kernel/rcu/tree_plugin.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index 340bbefe5f65..1bb73466a8a9 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -28,8 +28,8 @@ static bool rcu_rdp_is_offloaded(struct rcu_data *rdp)
 		!(lockdep_is_held(&rcu_state.barrier_mutex) ||
 		  (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) ||
 		  rcu_lockdep_is_held_nocb(rdp) ||
-		  (rdp == this_cpu_ptr(&rcu_data) &&
-		   !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) ||
+		   (!(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible()) &&
+			rdp == this_cpu_ptr(&rcu_data)) ||
 		  rcu_current_is_nocb_kthread(rdp)),
 		"Unsafe read of RCU_NOCB offloaded state"
 	);
-- 
2.17.1