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

["Christophe Leroy (CS GROUP)" <chleroy@kernel.org>]

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/


> 
> 
> 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)