Re:Re: [PATCH] irqchip: gic-v3-its: irq_pipeline: Fix OOB context in-band lock warning for ITS lock

At 2026-07-10 18:59:08, "Florian Bezdeka" <[email protected]> wrote:
>On Fri, 2026-07-10 at 12:12 +0200, Jan Kiszka wrote:
>> On 25.06.26 11:32, linz wrote:
>> > Hi, I find a call trace when I use v6.6.y-dovetail + xenomai v3.3 branch, the call trace is as follows
>> > 
>> > [    1.510903] IRQ pipeline: some code running in oob context 'Xenomai'
>> >                              called an in-band only routine
>> > [    1.510912] CPU: 0 PID: 0 Comm: swapper/0 Tainted: G S                 6.6.63-dovetail2 #8
>> > [    1.510918] Hardware name: Pe2204 DEMO DDR4 (DT)
>> > [    1.510920] IRQ stage: Xenomai
>> > [    1.510923] Call trace:
>> > [    1.510926]  dump_backtrace+0x90/0xe4
>> > [    1.510940]  show_stack+0x14/0x1c
>> > [    1.510946]  dump_stack_lvl+0x84/0xc8
>> > [    1.510953]  dump_stack+0x14/0x1c
>> > [    1.510957]  check_inband_stage+0xb0/0xc8
>> > [    1.510965]  inband_irq_save+0xc/0x28
>> > [    1.510971]  _raw_spin_lock_irqsave+0x14/0x90
>> > [    1.510977]  its_send_single_command+0x24/0x154
>> > [    1.510984]  lpi_update_config+0x9c/0x144
>> > [    1.510990]  its_mask_irq+0x2c/0x64
>> > [    1.510997]  irq_chip_mask_parent+0x18/0x20
>> > [    1.511005]  its_mask_msi_irq+0x1c/0x28
>> > [    1.511012]  handle_fasteoi_irq+0x1cc/0x2b4
>> > [    1.511016]  generic_pipeline_irq_desc+0x6c/0xa4
>> > [    1.511021]  generic_handle_domain_irq+0x18/0x20
>> > [    1.511028]  gic_handle_irq+0x4c/0x120
>> > [    1.511032]  handle_irq_pipelined+0x40/0x64
>> > [    1.511038]  call_on_irq_stack+0x24/0x30
>> > [    1.511044]  do_interrupt_handler+0x138/0x158
>> > [    1.511050]  el1_interrupt+0x40/0x110
>> > [    1.511055]  el1h_64_irq_handler+0x14/0x1c
>> > [    1.511061]  el1h_64_irq+0x64/0x68
>> > [    1.511064]  default_idle_call+0x30/0x78
>> > [    1.511071]  do_idle+0x128/0x150
>> > [    1.511077]  cpu_startup_entry+0x34/0x38
>> > [    1.511081]  kernel_init+0x0/0x1d4
>> > [    1.511088]  arch_post_acpi_subsys_init+0x0/0x8
>> > [    1.511096]  start_kernel+0x504/0x5cc
>> > [    1.511103]  __primary_switched+0xbc/0xc4
>> > 
>> > 
>> > The function call causing the issue is as follows:
>> > generic_handle_domain_irq
>> >     => generic_pipeline_irq_desc
>> >         => generic_handle_irq_desc
>> >             => handle_fasteoi_irq
>> >                 => mask_cond_eoi_irq
>> >                     => mask_irq
>> >                         => its_mask_msi_irq
>> >                             => irq_chip_mask_parent
>> >                                 => its_mask_irq
>> >                                     => lpi_update_config
>> >                                         => its_send_inv
>> >                                             => BUILD_SINGLE_CMD_FUNC
>> >                                                 => raw_spin_lock_irqsave(&its->lock, flags);
>> > 
>> > 
>> > On Dovetail-enabled kernels with Xenomai IRQ pipeline, GICv3 ITS interrupt handling runs in OOB (out-of-band) interrupt context. The original raw_spinlock_t used for its_node->lock invokes the standard in-band-only raw_spin_lock_irqsave() interface.
>> > This triggers the following pipeline context violation warning: IRQ pipeline: some code running in oob context 'Xenomai' called an in-band only routine
>> > 
>> > raw_spin_lock_irqsave() is an in-band exclusive API and cannot be safely called from Xenomai OOB interrupt context, which violates the IRQ pipeline isolation rules.
>> > 
>> > I think that fix this by replacing raw_spinlock_t with hybrid_spinlock_t for the ITS node lock. The hybrid spinlock supports both in-band Linux kernel context and OOB Xenomai pipeline context, adapting lock/irqsave logic dynamically according to the running context, eliminating the context mismatch warning while guaranteeing lock mutual exclusion.
>> > 
>> > The fixed up patch is as follows:
>> > 
>> > From 1037fcf6d75ecf37e1caf283d1198177e7410be3 Mon Sep 17 00:00:00 2001
>> > From: zhanglin <[email protected]>
>> > Date: Thu, 25 Jun 2026 16:56:31 +0800
>> > Subject: [PATCH] irqchip: gic-v3-its: irq_pipeline: fix OOB context in-band
>> >  lock warning for ITS lock
>> > 
>> > ---
>> >  drivers/irqchip/irq-gic-v3-its.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> > 
>> > diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> > index 0e57735eac..847b008b71 100644
>> > --- a/drivers/irqchip/irq-gic-v3-its.c
>> > +++ b/drivers/irqchip/irq-gic-v3-its.c
>> > @@ -94,7 +94,7 @@ struct its_device;
>> >   * list.
>> >   */
>> >  struct its_node {
>> > -    raw_spinlock_t        lock;
>> > +    hybrid_spinlock_t     lock;
>> >      struct mutex        dev_alloc_lock;
>> >      struct list_head    entry;
>> >      void __iomem        *base;
>> > -- 
>> > 2.34.1
>> > 
>> > Please help to review it, thank you.
>> 
>> Thanks for reporting.
>> 
>> Philippe, Florian, any comments on this?
>> 
>> Jan
>
>hybrid_spinlock_t doesn't look right at first glance, it's use should be
>limited to struct irq_desc and IRQ chips. I would have expected
>hard_spinlock_t, but I might miss something.
>
>Assuming the gic-v3 IRQ chip is already marked / flagged as
>IRQCHIP_PIPELINE_SAFE, right?
>
>Florian

>


Thank you for your feedback

The gic-v3 IRQ chip is already marked with IRQCHIP_PIPELINE_SAFE. 
The its_irq_chip is not marked with IRQCHIP_PIPELINE_SAFE. I added the flag and tested, but it did not have any effect.

Meanwhile, I read the code related to IRQCHIP_PIPELINE_SAFE. If the gic-v3 IRQ chip is not marked with IRQCHIP_PIPELINE_SAFE, a call trace like the following would be reported:
MSI domain irqchip XXX is not pipeline-safe! or irqchip XXX is not pipeline-safe!
However, I did not see any such message in dmsg logs.

Based on Florian's suggestion, I revisited the Xenomai 4 documentation regarding hybrid_spinlock_t and hard_spinlock_t. 
I agree with Florian's point that hybrid_spinlock_t should be limited to struct irq_desc and IRQ chips, and that hard_spinlock_t is more appropriate for the ITS node lock.

I changed the lock to hard_spinlock_t and tested it. The call trace no longer appears and the system works fine.

The patch is as follows. Please help review it:

From e0cbc9316af331bf007c86e1fcab0ef8699b05c9 Mon Sep 17 00:00:00 2001
From: zhanglin1040 <[email protected]>
Date: Mon, 13 Jul 2026 17:53:44 +0800
Subject: [PATCH] irqchip: gic-v3-its: irq_pipeline: fix OOB context in-band
 lock warning for ITS lock using hard spinlocks instead of hybrid spinlocks

---
 drivers/irqchip/irq-gic-v3-its.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
index 0e57735eac..3f2b02b8f4 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -94,7 +94,7 @@ struct its_device;
  * list.
  */
 struct its_node {
-    raw_spinlock_t        lock;
+    hard_spinlock_t        lock;
     struct mutex        dev_alloc_lock;
     struct list_head    entry;
     void __iomem        *base;
-- 
2.34.1