Re: [PATCH v4] debugobjects: Don't call fill_pool() in early boot hardirq context

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2026-06-03 15:52:50 [-0400], Waiman Long wrote:
> When booting a debug PREEMPT_RT kernel on an arm64 system with grace
> processor, the following lockdep warning 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
>     :
>   Call trace:
>     :
>    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+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
>     :

I would strip that backtrace since it is obvious from the description
below.

> During early boot, interrupts are getting enabled before the scheduler
> is enabled. In this window (before SYSTEM_SCHEDULING is set) interrupts
> can fire and attempt to fill the pool from within the hardirq. This can
> lead to a deadlock the interrupt occurred while in the memory allocator.
> 
> Add a new can_fill_pool() helper and reorder the exception rule and
> forbid this scenario by excluding allocations from hardirq.
> 
> Fixes: 06e0ae988f6e ("debugobjects: Allow to refill the pool before SYSTEM_SCHEDULING")
> Co-developed-by: Waiman Long <longman@redhat.com>
> Co-developed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Co-developed-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: Waiman Long <longman@redhat.com>

Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

Sebastian