rcutree_report_cpu_starting() must be called before cpu_probe() to avoid the following lockdep splat that triggered by calling __alloc_pages() when CONFIG_PROVE_RCU_LIST=y:

============================= WARNING: suspicious RCU usage 6.6.0+ #980 Not tainted ----------------------------- kernel/locking/lockdep.c:3761 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 1 lock held by swapper/1/0: #0: 900000000c82ef98 (&pcp->lock){+.+.}-{2:2}, at: get_page_from_freelist+0x894/0x1790 CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.6.0+ #980 Stack : 0000000000000001 9000000004f79508 9000000004893670 9000000100310000 90000001003137d0 0000000000000000 90000001003137d8 9000000004f79508 0000000000000000 0000000000000001 0000000000000000 90000000048a3384 203a656d616e2065 ca43677b3687e616 90000001002c3480 0000000000000008 000000000000009d 0000000000000000 0000000000000001 80000000ffffe0b8 000000000000000d 0000000000000033 0000000007ec0000 13bbf50562dad831 9000000005140748 0000000000000000 9000000004f79508 0000000000000004 0000000000000000 9000000005140748 90000001002bad40 0000000000000000 90000001002ba400 0000000000000000 9000000003573ec8 0000000000000000 00000000000000b0 0000000000000004 0000000000000000 0000000000070000 ... Call Trace: [<9000000003573ec8>] show_stack+0x38/0x150 [<9000000004893670>] dump_stack_lvl+0x74/0xa8 [<900000000360d2bc>] lockdep_rcu_suspicious+0x14c/0x190 [<900000000361235c>] __lock_acquire+0xd0c/0x2740 [<90000000036146f4>] lock_acquire+0x104/0x2c0 [<90000000048a955c>] _raw_spin_lock_irqsave+0x5c/0x90 [<900000000381cd5c>] rmqueue_bulk+0x6c/0x950 [<900000000381fc0c>] get_page_from_freelist+0xd4c/0x1790 [<9000000003821c6c>] __alloc_pages+0x1bc/0x3e0 [<9000000003583b40>] tlb_init+0x150/0x2a0 [<90000000035742a0>] per_cpu_trap_init+0xf0/0x110 [<90000000035712fc>] cpu_probe+0x3dc/0x7a0 [<900000000357ed20>] start_secondary+0x40/0xb0 [<9000000004897138>] smpboot_entry+0x54/0x58

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: Huacai Chen chenhuacai@loongson.cn --- arch/loongarch/kernel/smp.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/loongarch/kernel/smp.c b/arch/loongarch/kernel/smp.c index d19c2ebdf47b..1b5f266813a2 100644 --- a/arch/loongarch/kernel/smp.c +++ b/arch/loongarch/kernel/smp.c @@ -504,8 +504,9 @@ asmlinkage void start_secondary(void) unsigned int cpu;

sync_counter(); - cpu = smp_processor_id(); + cpu = raw_smp_processor_id(); set_my_cpu_offset(per_cpu_offset(cpu)); + rcu_cpu_starting(cpu);

cpu_probe(); constant_clockevent_init();