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From: Stefan Wiehler <stefan.wiehler@nokia.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Florian Fainelli <f.fainelli@gmail.com>,
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	Stefan Wiehler <stefan.wiehler@nokia.com>,
	Huacai Chen <chenhuacai@loongson.cn>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Subject: [PATCH] mips/smp: Call rcu_cpu_starting() earlier
Date: Fri, 19 Jan 2024 17:38:11 +0100
Message-ID: <20240119163811.3884999-1-stefan.wiehler@nokia.com>
In-Reply-To: <2024011935-snowman-regain-b820@gregkh>
References: <2024011935-snowman-regain-b820@gregkh>
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rcu_cpu_starting() must be called before clockevents_register_device() to avoid
the following lockdep splat triggered by calling list_add() when
CONFIG_PROVE_RCU_LIST=y:

  WARNING: suspicious RCU usage
  ...
  -----------------------------
  kernel/locking/lockdep.c:3680 RCU-list traversed in non-reader section!!

  other info that might help us debug this:

  RCU used illegally from offline CPU!
  rcu_scheduler_active = 1, debug_locks = 1
  no locks held by swapper/1/0.
  ...
  Call Trace:
  [<ffffffff8012a434>] show_stack+0x64/0x158
  [<ffffffff80a93d98>] dump_stack_lvl+0x90/0xc4
  [<ffffffff801c9e9c>] __lock_acquire+0x1404/0x2940
  [<ffffffff801cbf3c>] lock_acquire+0x14c/0x448
  [<ffffffff80aa4260>] _raw_spin_lock_irqsave+0x50/0x88
  [<ffffffff8021e0c8>] clockevents_register_device+0x60/0x1e8
  [<ffffffff80130ff0>] r4k_clockevent_init+0x220/0x3a0
  [<ffffffff801339d0>] start_secondary+0x50/0x3b8

raw_smp_processor_id() is required in order to avoid calling into lockdep
before RCU has declared the CPU to be watched for readers.

See also commit 29368e093921 ("x86/smpboot:  Move rcu_cpu_starting() earlier"),
commit de5d9dae150c ("s390/smp: move rcu_cpu_starting() earlier") and commit
99f070b62322 ("powerpc/smp: Call rcu_cpu_starting() earlier").

Signed-off-by: Stefan Wiehler <stefan.wiehler@nokia.com>
Reviewed-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
---
 arch/mips/kernel/smp.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 8fbef537fb88..81f6c4f8fbc1 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -351,10 +351,11 @@ early_initcall(mips_smp_ipi_init);
  */
 asmlinkage void start_secondary(void)
 {
-	unsigned int cpu;
+	unsigned int cpu = raw_smp_processor_id();
 
 	cpu_probe();
 	per_cpu_trap_init(false);
+	rcu_cpu_starting(cpu);
 	mips_clockevent_init();
 	mp_ops->init_secondary();
 	cpu_report();
@@ -366,7 +367,6 @@ asmlinkage void start_secondary(void)
 	 */
 
 	calibrate_delay();
-	cpu = smp_processor_id();
 	cpu_data[cpu].udelay_val = loops_per_jiffy;
 
 	set_cpu_sibling_map(cpu);
-- 
2.42.0