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Wed, 03 Jun 2026 15:53:13 -0400 X-MC-Unique: JT3gD-fNOQup8IDiTUsSAQ-1 X-Mimecast-MFC-AGG-ID: JT3gD-fNOQup8IDiTUsSAQ_1780516392 Received: from mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.95]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id C45041800599; Wed, 3 Jun 2026 19:53:11 +0000 (UTC) Received: from llong-thinkpadp16vgen1.westford.csb (unknown [10.22.89.171]) by mx-prod-int-10.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTP id E3BB81624; Wed, 3 Jun 2026 19:53:09 +0000 (UTC) From: Waiman Long To: Thomas Gleixner , Andrew Morton , Sebastian Andrzej Siewior , Clark Williams , Steven Rostedt Cc: linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Waiman Long Subject: [PATCH v4] debugobjects: Don't call fill_pool() in early boot hardirq context Date: Wed, 3 Jun 2026 15:52:50 -0400 Message-ID: <20260603195250.362595-1-longman@redhat.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.6 on 10.30.177.95 Content-Type: text/plain; charset="utf-8" When booting a debug PREEMPT_RT kernel on an arm64 system with grace processor, the following lockdep warning was reported during early boot. =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+0= x74/0xa0 : 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 : 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 Co-developed-by: Sebastian Andrzej Siewior Co-developed-by: Thomas Gleixner Signed-off-by: Waiman Long Reviewed-by: Sebastian Andrzej Siewior --- lib/debugobjects.c | 46 +++++++++++++++++++++++++++++++++++++--------- 1 file changed, 37 insertions(+), 9 deletions(-) diff --git a/lib/debugobjects.c b/lib/debugobjects.c index b18a682fe3da..6fb00e08a4e2 100644 --- a/lib/debugobjects.c +++ b/lib/debugobjects.c @@ -720,6 +720,41 @@ static inline bool debug_objects_is_pi_blocked_on(void) #endif } =20 +static inline bool can_fill_pool(void) +{ + /* + * On !RT enabled kernels there are no restrictions and spinlock_t and + * raw_spinlock_t are the same types. + */ + if (!IS_ENABLED(CONFIG_PREEMPT_RT)) + return true; + + /* + * On RT enabled kernels, the task must not be blocked on a lock as + * that could corrupt the PI state when blocking on a lock in the + * allocation path. + */ + if (debug_objects_is_pi_blocked_on()) + return false; + + /* + * On RT enabled kernels the pool refill should happen in preemptible + * context. + */ + if (preemptible()) + return true; + + /* + * Though during system boot before scheduling is set up, preemption is + * disabled and the pool can get exhausted. Before scheduling is active + * a task cannot be blocked on a sleeping lock, but it might hold a lock + * and if interrupted then hard interrupt context might run into a lock + * inversion. So exclude hard interrupt context from allocations before + * scheduling is active. + */ + return system_state < SYSTEM_SCHEDULING && !in_hardirq(); +} + static void debug_objects_fill_pool(void) { if (!static_branch_likely(&obj_cache_enabled)) @@ -734,18 +769,11 @@ static void debug_objects_fill_pool(void) if (likely(!pool_should_refill(&pool_global))) return; =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. - */ - if (!IS_ENABLED(CONFIG_PREEMPT_RT) || system_state < SYSTEM_SCHEDULING || - (preemptible() && !debug_objects_is_pi_blocked_on())) { + if (can_fill_pool()) { /* * Annotate away the spinlock_t inside raw_spinlock_t warning * by temporarily raising the wait-type to LD_WAIT_CONFIG, matching - * the preemptible() condition above. + * the preemptible() condition in can_fill_pool(). */ static DEFINE_WAIT_OVERRIDE_MAP(fill_pool_map, LD_WAIT_CONFIG); lock_map_acquire_try(&fill_pool_map); --=20 2.54.0