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Wed, 03 Jun 2026 10:59:58 -0400 X-MC-Unique: neE4Ee8nPhmgU4hhJKL0FQ-1 X-Mimecast-MFC-AGG-ID: neE4Ee8nPhmgU4hhJKL0FQ_1780498797 Received: from mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.12]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-06.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 207ED180035C; Wed, 3 Jun 2026 14:59:57 +0000 (UTC) Received: from [10.17.16.204] (unknown [10.17.16.204]) by mx-prod-int-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id D41B9195E483; Wed, 3 Jun 2026 14:59:55 +0000 (UTC) Message-ID: Date: Wed, 3 Jun 2026 10:59:55 -0400 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH-tip v3] debugobjects: Don't call fill_pool() in early boot non-task context To: Sebastian Andrzej Siewior Cc: Thomas Gleixner , Andrew Morton , Clark Williams , Steven Rostedt , linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev References: <20260520201509.931905-1-longman@redhat.com> <20260603075656.S1aZM9PO@linutronix.de> Content-Language: en-US From: Waiman Long In-Reply-To: <20260603075656.S1aZM9PO@linutronix.de> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.0 on 10.30.177.12 On 6/3/26 3:56 AM, Sebastian Andrzej Siewior wrote: > 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. >> >> ================================ >> 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. > > Reorder the exception rule and forbid this scenario by excluding > allocations from hardirq. Yes, the debug_objects_is_pi_blocked_on() check should cover the system_state check as well. > > … >> Fixes: 06e0ae988f6e ("debugobjects: Allow to refill the pool before SYSTEM_SCHEDULING") >> Signed-off-by: Waiman Long >> --- > … >> /* >> * 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) > > /* > * 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 I guess softirq won't be active during early boot. If in_nmi() is true, we are screwed for non-RT kernel as well. So only checking for in_hardirq() should be fine. I will adopt your suggestion and send a new version. Thanks, Longman > Sebastian >