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);
<Interrupt>
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:
21bbbc50f3 ("irqchip/gic-v3: Switch high priority PPIs over to handle_percpu_devid_irq()")
5ff78c8de9 ("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: fd7400cfcb ("genirq/chip: Invoke add_interrupt_randomness() in handle_percpu_devid_irq()")
Reported-by: Ada Couprie Diaz <ada.coupriediaz@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
Reviewed-by: Jinjie Ruan <ruanjinjie@huawei.com>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Link: https://patch.msgid.link/20260507110518.3128248-1-mark.rutland@arm.com
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