Re: [PATCH] powerpc/entry: Use hard_irq_disable() in arch_interrupt_exit_prepare()

[Venkat Rao Bagalkote <venkat88@linux.ibm.com>]

On 13/08/26 12:12 pm, Christophe Leroy (CS GROUP) wrote:
>
>
> Le 13/08/2026 à 08:36, Venkat Rao Bagalkote a écrit :
>>
>> On 12/08/26 8:50 pm, Mukesh Kumar Chaurasiya (IBM) wrote:
>>> commit 334f3f6d7a16 ("powerpc/entry: Disable interrupts before 
>>> irqentry_exit")
>>> fixed a BUG in preempt_schedule_irq() by calling local_irq_disable()
>>> unconditionally in arch_interrupt_exit_prepare() before 
>>> irqentry_exit().
>>> The fix is correct in intent but uses the wrong primitive for PPC64.
>>>
>>> On PPC64, local_irq_disable() only sets the soft-mask
>>> (irq_soft_mask = IRQS_DISABLED). It does not set PACA_IRQ_HARD_DIS in
>>> irq_happened and does not clear MSR[EE].
>>>
>>> This causes a continuous WARN_ON boot hang on Power11 pSeries LPARs
>>> using the dedicated-cede cpuidle path. When the CPU wakes from H_CEDE,
>>> interrupt_exit_kernel_prepare() calls replay_soft_interrupts(), which
>>> dispatches pending async handlers (timer_interrupt, do_IRQ) using the
>>> DEFINE_INTERRUPT_HANDLER_ASYNC macro. That macro calls
>>> arch_interrupt_async_exit_prepare() -> arch_interrupt_exit_prepare()
>>> before irqentry_exit(). With local_irq_disable(), PACA_IRQ_HARD_DIS
>>> is not set, but next_interrupt() unconditionally asserts it:
>>>
>>>    WARN_ON(!(local_paca->irq_happened & PACA_IRQ_HARD_DIS));
>>>
>>> This fires on every replayed interrupt, looping indefinitely and
>>> preventing boot completion.
>>>
>>> Fix this by replacing local_irq_disable() with hard_irq_disable().
>>> On PPC64, hard_irq_disable() sets irq_soft_mask to IRQS_ALL_DISABLED,
>>> sets PACA_IRQ_HARD_DIS in irq_happened, and clears MSR[EE] — satisfying
>>> all of:
>>>
>>>    - lockdep_assert_irqs_disabled() in irqentry_exit_to_kernel_mode()
>>>    - next_interrupt()'s WARN_ON(!(irq_happened & PACA_IRQ_HARD_DIS))
>>>    - preempt_schedule_irq()'s BUG_ON(!irqs_disabled())
>>>
>>> On PPC32/non-64, hard_irq_disable() is equivalent to 
>>> local_irq_disable(),
>>> so there is no regression on those platforms.
>>>
>>> Fixes: 334f3f6d7a16 ("powerpc/entry: Disable interrupts before 
>>> irqentry_exit")
>>> Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
>>> Closes: https://eur01.safelinks.protection.outlook.com/? 
>>> url=https%3A%2F%2Flore.kernel.org%2Fall%2F6f9bfb0f-b14c-468e-bb9f- 
>>> c157d120d0dc%40linux.ibm.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cf780f6a2abcf425c875808def90533e4%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C639221997929524168%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=kOer%2B610LkQs0ZKBn%2FutIB6j1bMoFasK4DmX4AEWOXA%3D&reserved=0 
>>>
>>> Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <mkchauras@gmail.com>
>>> ---
>>
>>
>> Tested this, and it fixes the reported issue.
>>
>> Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
>
> Didn't you say yesterday [1] that the change doesn't fix the issue ? 
> Did I miss something ?
>
> [1] 
> https://lore.kernel.org/all/2f7e6c34-7258-4b20-a38e-cedebccb835f@linux.ibm.com/ 
>
>
>
Hi Christophe,

I think there are two separate issues being mixed together here, both of 
which were reported by me.

The first issue is the early boot hang. I tested the patch in that 
context and reported that the boot hang still persisted.

The second issue is the WARN in __replay_soft_interrupts(). For that 
issue, the same patch fixes the problem, which is why I provided the 
Tested-by tag.

I believe the confusion comes from the fact that the same patch ended up 
being discussed in relation to both reports. My earlier comment that the 
patch did not fix the issue was referring to the boot hang, while my 
Tested-by was for the WARN in __replay_soft_interrupts().

So, to clarify:

Boot hang issue: not fixed by the patch.
WARN in __replay_soft_interrupts(): fixed by the patch.

Regards,
Venkat


>>
>>
>> Regards,
>>
>> Venkat.
>>
>>
>>> arch/powerpc/include/asm/entry-common.h | 2 +-
>>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>>
>>> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/ 
>>> include/asm/entry-common.h
>>> index c5adb5006361..de64389b0815 100644
>>> --- a/arch/powerpc/include/asm/entry-common.h
>>> +++ b/arch/powerpc/include/asm/entry-common.h
>>> @@ -270,7 +270,7 @@ static inline void 
>>> arch_interrupt_exit_prepare(struct pt_regs *regs)
>>>       }
>>>       /* irqentry_exit expects to be called with interrupts disabled */
>>> -    local_irq_disable();
>>> +    hard_irq_disable();
>>>   }
>>>   static inline void arch_interrupt_async_enter_prepare(struct 
>>> pt_regs *regs)
>