[PATCH v2] mips: mm: Call rcutree_report_cpu_starting() even earlier

[Stefan Wiehler]

rcutree_report_cpu_starting() must be called on secondary CPUs before
allocating memory to avoid the following Lockdep-RCU splat when
CONFIG_PROVE_RCU_LIST=y:

  WARNING: suspicious RCU usage
  6.6.119-00d46e15c416-fct #1 Not tainted
  -----------------------------
  /kernel/locking/lockdep.c:3762 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.

  stack backtrace:
  CPU: 1 PID: 0 Comm: swapper/1 Not tainted 6.6.119-00d46e15c416-fct #1
  Stack : 80000000029e37d8 0000000000000000 0000000000000008 80000000029e37e8
          80000000029e37e8 80000000029e3978 0000000000000000 0000000000000000
          0000000000000000 0000000000000001 ffffffff80d9df38 ffffffff810e19c0
          0000000000000000 0000000000000010 ffffffff80a7d140 0000000000000000
          ffffffff81c20814 0000000000000000 ffffffff80da0000 0000000000000000
          ffffffff80cadf38 0000000000000000 0000000000000000 80000000029ab680
          72f093276415c1f3 ffffffff81c2084f ffffffff80da0000 ffffffffc0149ed8
          fffffffffffffffe 80000000029e0000 80000000029e37e0 80000000029abf58
          ffffffff80129fb0 0000000000000000 0000000000000000 0000000000000000
          0000000000000000 0000000000000000 ffffffff80129fd0 0000000000000000
          ...
  Call Trace:
  [<ffffffff80129fd0>] show_stack+0x60/0x158
  [<ffffffff80a8cd84>] dump_stack_lvl+0x88/0xbc
  [<ffffffff801c78f8>] lockdep_rcu_suspicious+0x1c0/0x240
  [<ffffffff801cc80c>] __lock_acquire+0x121c/0x29d8
  [<ffffffff801ce14c>] lock_acquire+0x184/0x448
  [<ffffffff80a9ba30>] _raw_spin_lock_irqsave+0x50/0x90
  [<ffffffff80367038>] ___slab_alloc+0xa08/0x1808
  [<ffffffff80367e70>] __slab_alloc.isra.0+0x38/0x78
  [<ffffffff8036b7d4>] __kmem_cache_alloc_node+0x35c/0x370
  [<ffffffff80308ed8>] __kmalloc+0x58/0xd0
  [<ffffffff80a8f064>] r4k_tlb_uniquify+0x7c/0x428
  [<ffffffff80143e8c>] tlb_init+0x7c/0x110
  [<ffffffff8012bdb4>] per_cpu_trap_init+0x16c/0x1d0
  [<ffffffff80133258>] start_secondary+0x28/0x128

See also commit 55702ec9603e ("mips/smp: Call
rcutree_report_cpu_starting() earlier").

Fixes: 231ac951faba ("MIPS: mm: kmalloc tlb_vpn array to avoid stack overflow")
Signed-off-by: Stefan Wiehler <stefan.wiehler@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
V1 -> V2: Reorder rcutree_report_cpu_starting() call in
start_secondary(), fix function name

v1: https://patchwork.kernel.org/project/linux-mips/patch/20260407083324.906742-2-stefan.wiehler@xxxxxxxxx/
---
 arch/mips/kernel/smp.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/mips/kernel/smp.c b/arch/mips/kernel/smp.c
index 4868e79f3b30..bdb47c70d4f5 100644
--- a/arch/mips/kernel/smp.c
+++ b/arch/mips/kernel/smp.c
@@ -359,8 +359,8 @@ asmlinkage void start_secondary(void)
 	unsigned int cpu = raw_smp_processor_id();
 
 	cpu_probe();
-	per_cpu_trap_init(false);
 	rcutree_report_cpu_starting(cpu);
+	per_cpu_trap_init(false);
 	mips_clockevent_init();
 	mp_ops->init_secondary();
 	cpu_report();
-- 
2.42.0