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charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <20260520201509.931905-1-longman@redhat.com> On 2026-05-20 16:15:09 [-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. >=20 > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D > 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 > : What about: 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. =20 Reorder the exception rule and forbid this scenario by excluding allocations from hardirq. =E2=80=A6 > Fixes: 06e0ae988f6e ("debugobjects: Allow to refill the pool before SYSTE= M_SCHEDULING") > Signed-off-by: Waiman Long > --- =E2=80=A6 > /* > * On RT enabled kernels the pool refill must happen in preemptible > - * context and not enqueued on an rt_mutex -- 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. > + * context and not enqueued on an rt_mutex or in task context during > + * early boot before scheduling starts. > + * > + * 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) || system_state < SYSTEM_SCHEDULING = || > + if (!IS_ENABLED(CONFIG_PREEMPT_RT) || > + (system_state < SYSTEM_SCHEDULING && in_task()) || > (preemptible() && !debug_objects_is_pi_blocked_on())) { > /* > * Annotate away the spinlock_t inside raw_spinlock_t warning I updated the comment to explain in more verbose why this and that is done. I re-ordered the whole thing stared with the pi-locked-on part since this is always valid. It shouldn't happen during early boot I think it is easier to read that way. Then we restrict it to the preeptible case which can be overruled with the SYSTEM_SCHEDULING exception however as long as it is not an hardirq. It looks easier to parse and hopefully brings an end to this. diff --git a/lib/debugobjects.c b/lib/debugobjects.c index b18a682fe3da2..2adfe2a79a086 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -736,12 +736,17 @@ static void debug_objects_fill_pool(void) =20 /* * On RT enabled kernels the pool refill must happen in preemptible - * context and not enqueued on an rt_mutex -- 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. + * context and not while blocking on a lock which can trigger recursion + * during PI. During system boot (before scheduling) preemption is + * disabled and the pool gets exhausted. Without scheduling a deadlock + * is not possible if allocations from interrupt context are excluded. + * 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) || system_state < SYSTEM_SCHEDULING || - (preemptible() && !debug_objects_is_pi_blocked_on())) { + if (!IS_ENABLED(CONFIG_PREEMPT_RT) || + !debug_objects_is_pi_blocked_on() && + (preemptible() || (system_state < SYSTEM_SCHEDULING && !in_hardirq())= )) { /* * Annotate away the spinlock_t inside raw_spinlock_t warning * by temporarily raising the wait-type to LD_WAIT_CONFIG, matching Sebastian