[PATCH AUTOSEL 6.6 36/47] mips/smp: Call rcutree_report_cpu_starting() earlier

Sasha Levin
2023-12-11T13:55:11Z

From: Stefan Wiehler <stefan.wiehler@nokia.com>

[ Upstream commit 55702ec9603ebeffb15e6f7b113623fe1d8872f4 ]

rcutree_report_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>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 8fbef537fb885..82e2e051b4161 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);
+ rcutree_report_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