When booting a debug PREEMPT_RT kernel on an arm64 system with grace
processor, the following lockdep splat was reported during early boot.

  ================================
  WARNING: inconsistent lock state
  7.1.0-rc4-test+ #1 Not tainted
  --------------------------------
  inconsistent {HARDIRQ-ON-W} -> {IN-HARDIRQ-W} usage.
  swapper/0/0 [HC1[1]:SC0[0]:HE0:SE1] takes:
  ffff0000803346a0 (&n->list_lock){?.+.}-{3:3}, at: get_from_partial_node+0x74/0xa0
  {HARDIRQ-ON-W} state was registered at:
    __lock_acquire+0x3d4/0xb70
    lock_acquire.part.0+0x178/0x2e0
    lock_acquire+0xa0/0x240
    rt_spin_lock+0xa0/0x400
    __refill_objects_node+0x8c/0x638
    refill_objects+0x60/0x120
    __pcs_replace_empty_main+0x11c/0x3a8
    __kmalloc_noprof+0x550/0x5e0
    __alloc_workqueue+0x7a4/0xb68
    alloc_workqueue_noprof+0xc0/0x118
    kmem_cache_init_late+0x3c/0xd8
    start_kernel+0x360/0x460
    __primary_switched+0x8c/0xa0
  irq event stamp: 12818
  hardirqs last  enabled at (12817): [<ffffda0f4322be98>] __raw_spin_unlock_irqrestore+0xb8/0xe8
  hardirqs last disabled at (12818): [<ffffda0f45a611f4>] el1_interrupt+0x34/0xb0
  softirqs last  enabled at (0): [<0000000000000000>] 0x0
  softirqs last disabled at (0): [<0000000000000000>] 0x0
    :
  Call trace:
   show_stack+0x20/0x40 (C)
   dump_stack_lvl+0x7c/0x160
   dump_stack+0x1c/0x48
   print_usage_bug.part.0+0x248/0x270
   mark_lock_irq+0x410/0x608
   mark_lock+0x1ec/0x3a8
   mark_usage+0x138/0x170
   __lock_acquire+0x3d4/0xb70
   lock_acquire.part.0+0x178/0x2e0
   lock_acquire+0xa0/0x240
   rt_spin_lock+0xa0/0x400
   get_from_partial_node+0x74/0xa0
   ___slab_alloc+0x94/0x4f8
   kmem_cache_alloc_noprof+0x2d4/0x598
   kmem_alloc_batch+0x54/0x170
   fill_pool+0x12c/0x438
   debug_objects_fill_pool.part.0+0x88/0x100
   debug_objects_fill_pool+0x58/0x60
   debug_object_activate+0xfc/0x3d0
   add_timer_on+0x250/0x3a0
   add_interrupt_randomness+0x2d4/0x340
   handle_percpu_devid_irq+0x2e0/0x4e0
   handle_irq_desc+0xc0/0x120
   generic_handle_domain_irq+0x20/0x40
   __gic_handle_irq_from_irqson.isra.0+0x3c4/0x708
   gic_handle_irq+0x7c/0xe0
   call_on_irq_stack+0x30/0x48
   do_interrupt_handler+0x134/0x158
   el1_interrupt+0x48/0xb0
   el1h_64_irq_handler+0x18/0x28
   el1h_64_irq+0x80/0x88

The {IN-HARDIRQ-W} usage happens when debug_objects_fill_pool() calls
fill_pool() in the hardirq context during early boot. It is because of
the "system_state < SYSTEM_SCHEDULING" check in debug_objects_fill_pool()
which allows fill_pool() to be called from any context during early
boot.

Calling fill_pool() from any context is problematic as deadlock can
happen even though the early boot window should be pretty short. Fix
that by restricting the call to only in_task() context during early boot.

Fixes: 06e0ae988f6e ("debugobjects: Allow to refill the pool before SYSTEM_SCHEDULING")
Signed-off-by: Waiman Long <longman@redhat.com>
---
 lib/debugobjects.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/lib/debugobjects.c b/lib/debugobjects.c
index 12e2e42e6a31..236ea5e716df 100644
--- a/lib/debugobjects.c
+++ b/lib/debugobjects.c
@@ -727,11 +727,14 @@ static void debug_objects_fill_pool(void)
 
 	/*
 	 * On RT enabled kernels the pool refill must happen in preemptible
-	 * context -- for !RT kernels we rely on the fact that spinlock_t and
+	 * context or in task context during early boot.
+	 *
+	 * For !RT kernels we rely on the fact that spinlock_t and
 	 * raw_spinlock_t are basically the same type and this lock-type
 	 * inversion works just fine.
 	 */
-	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible() || system_state < SYSTEM_SCHEDULING) {
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT) || preemptible() ||
+	   (system_state < SYSTEM_SCHEDULING && in_task())) {
 		/*
 		 * Annotate away the spinlock_t inside raw_spinlock_t warning
 		 * by temporarily raising the wait-type to LD_WAIT_CONFIG, matching
-- 
2.54.0