[PATCH v2] irqchip/gic-v3-its: Remove cpumask_var_t allocation

From: Pierre Gondois
Date: Mon Sep 12 2022 - 10:19:24 EST

Running a preemp_rt kernel based on v5.19-rc3-rt4 on an Ampere Altra
triggers:
[ 22.616229] BUG: sleeping function called from invalid context at kernel/locking/spinlock_rt.c:46
[ 22.616239] in_atomic(): 1, irqs_disabled(): 128, non_block: 0, pid: 1884, name: kworker/80:1
[ 22.616243] preempt_count: 3, expected: 0
[ 22.616244] RCU nest depth: 0, expected: 0
[...]
[ 22.616250] hardirqs last enabled at (33): _raw_spin_unlock_irq (/home/piegon01/linux/./arch/arm64/include/asm/irqflags.h:35)
[ 22.616273] hardirqs last disabled at (34): __schedule (/home/piegon01/linux/kernel/sched/core.c:6432 (discriminator 1))
[ 22.616283] softirqs last enabled at (0): copy_process (/home/piegon01/linux/./include/linux/lockdep.h:191)
[ 22.616297] softirqs last disabled at (0): 0x0
[ 22.616305] Preemption disabled at:
[ 22.616307] __setup_irq (/home/piegon01/linux/kernel/irq/manage.c:1612)
[ 22.616322] CPU: 80 PID: 1884 Comm: kworker/80:1 Tainted: G W [...]
[ 22.616328] Hardware name: WIWYNN Mt.Jade Server System B81.03001.0005/Mt.Jade Motherboard, BIOS 1.08.20220218 (SCP: 1.08.20220218) 2022/02/18
[ 22.616333] Workqueue: events work_for_cpu_fn
[ 22.616344] Call trace:
[...]
[ 22.616403] alloc_cpumask_var_node (/home/piegon01/linux/lib/cpumask.c:115)
[ 22.616414] alloc_cpumask_var (/home/piegon01/linux/lib/cpumask.c:147)
[ 22.616417] its_select_cpu (/home/piegon01/linux/drivers/irqchip/irq-gic-v3-its.c:1580)
[ 22.616428] its_set_affinity (/home/piegon01/linux/drivers/irqchip/irq-gic-v3-its.c:1659)
[ 22.616431] msi_domain_set_affinity (/home/piegon01/linux/kernel/irq/msi.c:501)
[ 22.616440] irq_do_set_affinity (/home/piegon01/linux/kernel/irq/manage.c:276)
[ 22.616443] irq_setup_affinity (/home/piegon01/linux/kernel/irq/manage.c:633)
[ 22.616447] irq_startup (/home/piegon01/linux/kernel/irq/chip.c:280)
[ 22.616453] __setup_irq (/home/piegon01/linux/kernel/irq/manage.c:1777)

commit cba4235e6031e ("genirq: Remove mask argument from
setup_affinity()")
and
commit 11ea68f553e24 ("genirq, sched/isolation: Isolate from handling
managed interrupts")
overcome this issue by defining a static struct cpumask and protecting
it by a raw spinlock. The code in these commits is executed with IRQs
disabled.

its_select_cpu() can be executed with IRQs enabled or disabled.
Disabling IRQs with raw_spin_lock_irqsave() is necessary to avoid a:
'WARNING: possible irq lock inversion dependency detected'
[ 2.935126] CPU0 CPU1
[ 2.935126] ---- ----
[ 2.935127] lock(tmpmask_lock);
[ 2.935129] local_irq_disable();
[ 2.935129] lock(&irq_desc_lock_class);
[ 2.935131] lock(tmp_mask_lock);
[ 2.935133] <Interrupt>
[ 2.935133] lock(&irq_desc_lock_class);
[...]
[ 2.935446] ... key at: tmpmask_lock.56732+0x18/0x40
[ 2.935451] ... acquired at:
[ 2.935452] _raw_spin_lock (linux/./include/linux/spinlock_api_smp.h:134)
[ 2.935454] its_select_cpu (linux/drivers/irqchip/irq-gic-v3-its.c:1584)
[ 2.935457] its_set_affinity (linux/drivers/irqchip/irq-gic-v3-its.c:1661)
[ 2.935460] msi_domain_set_affinity (linux/kernel/irq/msi.c:501)
[ 2.935463] irq_do_set_affinity (linux/kernel/irq/manage.c:276)
[ 2.935468] irq_setup_affinity (linux/kernel/irq/manage.c:633)
[ 2.935471] irq_startup (linux/kernel/irq/chip.c:280)
[ 2.935473] __setup_irq (linux/kernel/irq/manage.c:1777)
[ 2.935476] request_threaded_irq (linux/kernel/irq/manage.c:2206)
[...]
[ 2.935592] ... key at: tmp_mask_lock.40873+0x18/0x40
[ 2.935598] ... acquired at:
[ 2.935598] _raw_spin_lock (linux/./include/linux/spinlock_api_smp.h:134)
[ 2.935600] irq_do_set_affinity (linux/./include/linux/irq.h:381)
[ 2.935603] irq_startup (linux/kernel/irq/chip.c:273)
[ 2.935605] __setup_irq (linux/kernel/irq/manage.c:1777)
[ 2.935608] request_threaded_irq (linux/kernel/irq/manage.c:2206)
[...]
[ 2.935812] ... key at: irq_desc_lock_class+0x0/0x10
[ 2.935819] ... acquired at:
[ 2.935820] __lock_acquire (linux/kernel/locking/lockdep.c:4524)
[ 2.935822] lock_acquire (linux/kernel/locking/lockdep.c:466)
[ 2.935823] _raw_spin_lock (linux/./include/linux/spinlock_api_smp.h:134)
[ 2.935825] handle_fasteoi_irq (linux/kernel/irq/chip.c:693)
[ 2.935827] generic_handle_domain_irq (linux/kernel/irq/irqdesc.c:649)
[ 2.935830] gic_handle_irq (linux/drivers/irqchip/irq-gic-v3.c:736)
[ 2.935832] call_on_irq_stack (linux/arch/arm64/kernel/entry.S:902)
[ 2.935834] do_interrupt_handler (linux/arch/arm64/kernel/entry-common.c:274)

Signed-off-by: Pierre Gondois <pierre.gondois@xxxxxxx>
---
drivers/irqchip/irq-gic-v3-its.c | 14 ++++++++------
1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 5ff09de6c48f..beead1a0191c 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -1574,13 +1574,15 @@ static int its_select_cpu(struct irq_data *d,
const struct cpumask *aff_mask)
{
struct its_device *its_dev = irq_data_get_irq_chip_data(d);
- cpumask_var_t tmpmask;
+ static DEFINE_RAW_SPINLOCK(tmpmask_lock);
+ static struct cpumask __tmpmask;
+ struct cpumask *tmpmask;
+ unsigned long flags;
int cpu, node;
-
- if (!alloc_cpumask_var(&tmpmask, GFP_ATOMIC))
- return -ENOMEM;
-
node = its_dev->its->numa_node;
+ tmpmask = &__tmpmask;
+
+ raw_spin_lock_irqsave(&tmpmask_lock, flags);

if (!irqd_affinity_is_managed(d)) {
/* First try the NUMA node */
@@ -1634,7 +1636,7 @@ static int its_select_cpu(struct irq_data *d,
cpu = cpumask_pick_least_loaded(d, tmpmask);
}
out:
- free_cpumask_var(tmpmask);
+ raw_spin_unlock_irqrestore(&tmpmask_lock, flags);

pr_debug("IRQ%d -> %*pbl CPU%d\n", d->irq, cpumask_pr_args(aff_mask), cpu);
return cpu;
--
2.25.1