Re: [PATCH v4] irqchip: gic-v3-its: irq_pipeline: Fix OOB context in-band lock warning for ITS lock

At 2026-08-04 16:59:00, "Florian Bezdeka" <[email protected]> wrote:
>On Tue, 2026-08-04 at 16:53 +0800, linz wrote:
>> The warning shown below could be observed on Dovetail 6.6 with arm64
>> architecture when CONFIG_DEBUG_IRQ_PIPELINE is enabled.
>> 
>> The reason is the usage of a raw_spinlock_t in hard IRQ masking code
>> path. A migration to hard_spinlock_t fixes this issue.
>> 
>> [    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
>> 
>> Beyond that, note that IRQ chip handlers such as irq_mask / irq_unmask run in
>> OOB context. For instance, any code path calling lpi_update_config() must
>> be oob‑capable, so gic_data_rdist_cpu(cpu)->rd_lock and its_vpe->vpe_lock are
>> modified in this patch.
>> 
>> Convert:
>> - its_node->lock
>> - rdists.rd_lock
>> - its_vpe->vpe_lock
>> from raw_spinlock_t to hard_spinlock_t.
>> 
>> Signed-off-by: linz <[email protected]>
>> ---
>>  drivers/irqchip/irq-gic-v3-its.c   | 2 +-
>>  include/linux/irqchip/arm-gic-v3.h | 2 +-
>>  include/linux/irqchip/arm-gic-v4.h | 2 +-
>>  3 files changed, 3 insertions(+), 3 deletions(-)
>> 
>> 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;
>> diff --git a/include/linux/irqchip/arm-gic-v3.h b/include/linux/irqchip/arm-gic-v3.h
>> index 7286913654..9dcbf4b331 100644
>> --- a/include/linux/irqchip/arm-gic-v3.h
>> +++ b/include/linux/irqchip/arm-gic-v3.h
>> @@ -613,7 +613,7 @@
>>  
>>  struct rdists {
>>      struct {
>> -        raw_spinlock_t    rd_lock;
>> +        hard_spinlock_t    rd_lock;
>>          void __iomem    *rd_base;
>>          struct page    *pend_page;
>>          phys_addr_t    phys_base;
>> diff --git a/include/linux/irqchip/arm-gic-v4.h b/include/linux/irqchip/arm-gic-v4.h
>> index bf9e064028..d7afd9d2cd 100644
>> --- a/include/linux/irqchip/arm-gic-v4.h
>> +++ b/include/linux/irqchip/arm-gic-v4.h
>> @@ -68,7 +68,7 @@ struct its_vpe {
>>       * Ensures mutual exclusion between affinity setting of the
>>       * vPE and vLPI operations using vpe->col_idx.
>>       */
>> -    raw_spinlock_t        vpe_lock;
>> +    hard_spinlock_t        vpe_lock;
>
>Can you please share the call stack where this lock is involved in an
>OOB code path?
>
>The other two locks are fine. I'm unsure about this one here.

>
The vpe_lock can be taken in OOB context via the following call chain when
handling vLPI interrupt masking:

its_mask_irq()
    lpi_update_config()
        direct_lpi_inv()
            __direct_lpi_inv()
                irq_to_cpuid_lock()
                    vpe_to_cpuid_lock()
                        raw_spin_lock_irqsave(&vpe->vpe_lock, *flags);

Since its_mask_irq() executes from the out‑of‑band stage
under Dovetail’s irq pipeline, raw_spinlock_t here would trigger the
CONFIG_DEBUG_IRQ_PIPELINE warning.

I have not physically observed a printed call trace for vpe_lock yet,
but code inspection confirms this lock is reachable from OOB context.
So I convert its_vpe->vpe_lock to hard_spinlock_t together with the
other two locks.
>>      /*
>>       * This collection ID is used to indirect the target
>>       * redistributor for this VPE. The ID itself isn't involved in
>> -- 
>> 2.34.1