From 512718bbc51b851140380b7068ec7365bd039cba Mon Sep 17 00:00:00 2001 From: Mark Rutland Date: Thu, 7 May 2026 12:05:18 +0100 Subject: [PATCH] genirq/chip: Don't call add_interrupt_randomness() for NMIs Recently handle_percpu_devid_irq() was changed to call add_interrupt_randomness(). This introduced a potential deadlock when handle_percpu_devid_irq() is used to handle an NMI, which can be detected with lockdep, e.g. ================================ WARNING: inconsistent lock state 7.1.0-rc2-pnmi #465 Not tainted -------------------------------- inconsistent {INITIAL USE} -> {IN-NMI} usage. perf/695 [HC1[1]:SC0[0]:HE0:SE1] takes: ffff00837dfd3a18 (&base->lock){-.-.}-{2:2}, at: lock_timer_base+0x6c/0xac {INITIAL USE} state was registered at: _raw_spin_lock_irqsave+0x68/0xb0 lock_timer_base+0x6c/0xac __mod_timer+0x100/0x32c add_timer_global+0x2c/0x40 __queue_delayed_work+0xf0/0x140 queue_delayed_work_on+0x134/0x138 mem_cgroup_css_online+0x30c/0x310 online_css+0x34/0x10c cgroup_init_subsys+0x158/0x1c8 cgroup_init+0x440/0x524 start_kernel+0x888/0x998 other info that might help us debug this: Possible unsafe locking scenario: CPU0 ---- lock(&base->lock); lock(&base->lock); *** DEADLOCK *** Call trace: _raw_spin_lock_irqsave+0x68/0xb0 lock_timer_base+0x6c/0xac add_timer_on+0x78/0x16c add_interrupt_randomness+0x124/0x134 handle_percpu_devid_irq+0xd4/0x16c handle_irq_desc+0x40/0x58 generic_handle_domain_nmi+0x28/0x50 __gic_handle_nmi.isra.0+0x4c/0xa0 gic_handle_irq+0x38/0x2bc call_on_irq_stack+0x30/0x48 do_interrupt_handler+0x80/0x98 el1_interrupt+0x90/0xac el1h_64_irq_handler+0x18/0x24 el1h_64_irq+0x80/0x84 [...] During review, Thomas pointed out it wouldn't be safe for handle_percpu_devid_irq() to call add_interrupt_randomness() if it was used to handle NMIs: https://lore.kernel.org/lkml/87bjgik042.ffs@tglx/ ... but evidently people missed that handle_percpu_devid_irq() *is* used for NMIs. While it might seem that NMIs should be handled with a separate handle_percpu_devid_nmi() function, for various structural reasons this was impractical, and handle_percpu_devid_irq() has been expected to be used for NMIs since commits: 21bbbc50f398f ("irqchip/gic-v3: Switch high priority PPIs over to handle_percpu_devid_irq()") 5ff78c8de9d83 ("genirq: Kill handle_percpu_devid_fasteoi_nmi()") Taking the above into account, avoid the deadlock by not calling add_interrupt_randomness() when handle_percpu_devid_irq() is called in an NMI context. This is consistent with other NNI handling flows, which do not call add_interrupt_randomness(). At the same time, update the kernel-doc comment to make it clear that handle_percpu_devid_irq() can be called in NMI context. The rest of handle_percpu_devid_irq() is currently NMI safe and doesn't need to change. Fixes: fd7400cfcbaa ("genirq/chip: Invoke add_interrupt_randomness() in handle_percpu_devid_irq()") Reported-by: Ada Couprie Diaz Signed-off-by: Mark Rutland Signed-off-by: Thomas Gleixner Reviewed-by: Jinjie Ruan Reviewed-by: Marc Zyngier Link: https://patch.msgid.link/20260507110518.3128248-1-mark.rutland@arm.com --- kernel/irq/chip.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c index 6c9b1dc4e7d4..b635e3c5d5b6 100644 --- a/kernel/irq/chip.c +++ b/kernel/irq/chip.c @@ -14,6 +14,7 @@ #include #include #include +#include #include #include @@ -893,7 +894,10 @@ void handle_percpu_irq(struct irq_desc *desc) * * action->percpu_dev_id is a pointer to percpu variables which * contain the real device id for the cpu on which this handler is - * called + * called. + * + * May be used for NMI interrupt lines, and so may be called in IRQ or NMI + * context. */ void handle_percpu_devid_irq(struct irq_desc *desc) { @@ -930,7 +934,8 @@ void handle_percpu_devid_irq(struct irq_desc *desc) enabled ? " and unmasked" : "", irq, cpu); } - add_interrupt_randomness(irq); + if (!in_nmi()) + add_interrupt_randomness(irq); if (chip->irq_eoi) chip->irq_eoi(&desc->irq_data);