[v1] powerpc/entry: Disable interrupts before irqentry_exit

[PATCH] powerpc/entry: Disable interrupts before irqentry_exit

Posted by Shrikanth Hegde 4 days, 20 hours ago

Venkat reported a panic on powerpc-next tree where GENERIC_ENTRY has
been enabled.

kernel BUG at kernel/sched/core.c:7512!
NIP  preempt_schedule_irq+0x44/0x118
LR   dynamic_irqentry_exit_cond_resched+0x40/0x1a4
Call Trace:
 dynamic_irqentry_exit_cond_resched+0x40/0x1a4
 do_page_fault+0xc0/0x104
 data_access_common_virt+0x210/0x220

This happens since __do_page_fault ends up enabling the interrupts and
it could take significant time such that need_resched could be set. This
leads to schedule call in irqentry_exit leading to the bug.

There are many such irq handlers which enables the interrupts.
Fix it by disabling the irq before calling irqentry_exit. The same
pattern exists today in interrupt_exit_kernel_prepare.

While there, make those BUG_ON into WARN_ON. Interrupt is disabled right
after so it is not that severe. This will still help to catch the
offending callsites.

Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
Closes: https://lore.kernel.org/all/7904105b-9dfa-4efd-a5ef-bc0276ed255d@linux.ibm.com/
Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
---

This applies on top on powerpc/next tree.
base: 6ed60999d33d '("powerpc: Remove unused functions")'

 arch/powerpc/include/asm/entry-common.h | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
index de5601282755..7da373a56813 100644
--- a/arch/powerpc/include/asm/entry-common.h
+++ b/arch/powerpc/include/asm/entry-common.h
@@ -253,16 +253,17 @@ static inline void arch_interrupt_enter_prepare(struct pt_regs *regs)
 static inline void arch_interrupt_exit_prepare(struct pt_regs *regs)
 {
 	if (user_mode(regs)) {
-		BUG_ON(regs_is_unrecoverable(regs));
-		BUG_ON(regs_irqs_disabled(regs));
+		WARN_ON(regs_is_unrecoverable(regs));
+		WARN_ON(regs_irqs_disabled(regs));
 		/*
 		 * We don't need to restore AMR on the way back to userspace for KUAP.
 		 * AMR can only have been unlocked if we interrupted the kernel.
 		 */
 		kuap_assert_locked();
-
-		local_irq_disable();
 	}
+
+	/* irqentry_exit expects to be called with interrupts disabled */
+	local_irq_disable();
 }
 
 static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs)
-- 
2.47.3

Re: [PATCH] powerpc/entry: Disable interrupts before irqentry_exit

Posted by Peter Zijlstra 4 days, 20 hours ago

On Wed, Jun 03, 2026 at 03:25:21PM +0530, Shrikanth Hegde wrote:
> Venkat reported a panic on powerpc-next tree where GENERIC_ENTRY has
> been enabled.
> 
> kernel BUG at kernel/sched/core.c:7512!
> NIP  preempt_schedule_irq+0x44/0x118
> LR   dynamic_irqentry_exit_cond_resched+0x40/0x1a4
> Call Trace:
>  dynamic_irqentry_exit_cond_resched+0x40/0x1a4
>  do_page_fault+0xc0/0x104
>  data_access_common_virt+0x210/0x220
> 
> This happens since __do_page_fault ends up enabling the interrupts and
> it could take significant time such that need_resched could be set. This
> leads to schedule call in irqentry_exit leading to the bug.
> 
> There are many such irq handlers which enables the interrupts.
> Fix it by disabling the irq before calling irqentry_exit. The same
> pattern exists today in interrupt_exit_kernel_prepare.
> 
> While there, make those BUG_ON into WARN_ON. Interrupt is disabled right
> after so it is not that severe. This will still help to catch the
> offending callsites.
> 
> Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
> Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
> Closes: https://lore.kernel.org/all/7904105b-9dfa-4efd-a5ef-bc0276ed255d@linux.ibm.com/
> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
> ---
> 
> This applies on top on powerpc/next tree.
> base: 6ed60999d33d '("powerpc: Remove unused functions")'
> 
>  arch/powerpc/include/asm/entry-common.h | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
> index de5601282755..7da373a56813 100644
> --- a/arch/powerpc/include/asm/entry-common.h
> +++ b/arch/powerpc/include/asm/entry-common.h
> @@ -253,16 +253,17 @@ static inline void arch_interrupt_enter_prepare(struct pt_regs *regs)
>  static inline void arch_interrupt_exit_prepare(struct pt_regs *regs)
>  {
>  	if (user_mode(regs)) {
> -		BUG_ON(regs_is_unrecoverable(regs));
> -		BUG_ON(regs_irqs_disabled(regs));
> +		WARN_ON(regs_is_unrecoverable(regs));
> +		WARN_ON(regs_irqs_disabled(regs));

So while you will indeed disable IRQs righ below. This checks the IRQ
state of regs, not the current state.

What you are allowing through it a *userspace* state that has IRQs
disabled. That is an invalid state.

>  		/*
>  		 * We don't need to restore AMR on the way back to userspace for KUAP.
>  		 * AMR can only have been unlocked if we interrupted the kernel.
>  		 */
>  		kuap_assert_locked();
> -
> -		local_irq_disable();
>  	}
> +
> +	/* irqentry_exit expects to be called with interrupts disabled */
> +	local_irq_disable();
>  }
>  
>  static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs)
> -- 
> 2.47.3
>

Re: [PATCH] powerpc/entry: Disable interrupts before irqentry_exit

Posted by Shrikanth Hegde 4 days, 18 hours ago

Hi Peter. Thanks for taking a look at it.

On 6/3/26 3:41 PM, Peter Zijlstra wrote:
> On Wed, Jun 03, 2026 at 03:25:21PM +0530, Shrikanth Hegde wrote:
>> Venkat reported a panic on powerpc-next tree where GENERIC_ENTRY has
>> been enabled.
>>
>> kernel BUG at kernel/sched/core.c:7512!
>> NIP  preempt_schedule_irq+0x44/0x118
>> LR   dynamic_irqentry_exit_cond_resched+0x40/0x1a4
>> Call Trace:
>>   dynamic_irqentry_exit_cond_resched+0x40/0x1a4
>>   do_page_fault+0xc0/0x104
>>   data_access_common_virt+0x210/0x220
>>
>> This happens since __do_page_fault ends up enabling the interrupts and
>> it could take significant time such that need_resched could be set. This
>> leads to schedule call in irqentry_exit leading to the bug.
>>
>> There are many such irq handlers which enables the interrupts.
>> Fix it by disabling the irq before calling irqentry_exit. The same
>> pattern exists today in interrupt_exit_kernel_prepare.
>>
>> While there, make those BUG_ON into WARN_ON. Interrupt is disabled right
>> after so it is not that severe. This will still help to catch the
>> offending callsites.
>>
>> Fixes: bee25f97ad24 ("powerpc: Enable GENERIC_ENTRY feature")
>> Reported-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>
>> Closes: https://lore.kernel.org/all/7904105b-9dfa-4efd-a5ef-bc0276ed255d@linux.ibm.com/
>> Signed-off-by: Shrikanth Hegde <sshegde@linux.ibm.com>
>> ---
>>
>> This applies on top on powerpc/next tree.
>> base: 6ed60999d33d '("powerpc: Remove unused functions")'
>>
>>   arch/powerpc/include/asm/entry-common.h | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
>> index de5601282755..7da373a56813 100644
>> --- a/arch/powerpc/include/asm/entry-common.h
>> +++ b/arch/powerpc/include/asm/entry-common.h
>> @@ -253,16 +253,17 @@ static inline void arch_interrupt_enter_prepare(struct pt_regs *regs)
>>   static inline void arch_interrupt_exit_prepare(struct pt_regs *regs)
>>   {
>>   	if (user_mode(regs)) {
>> -		BUG_ON(regs_is_unrecoverable(regs));
>> -		BUG_ON(regs_irqs_disabled(regs));
>> +		WARN_ON(regs_is_unrecoverable(regs));
>> +		WARN_ON(regs_irqs_disabled(regs));
> 
> So while you will indeed disable IRQs righ below. This checks the IRQ
> state of regs, not the current state.
> 
> What you are allowing through it a *userspace* state that has IRQs
> disabled. That is an invalid state.

Ok. I should have seen it closely. Let me keep them as is.

> 
>>   		/*
>>   		 * We don't need to restore AMR on the way back to userspace for KUAP.
>>   		 * AMR can only have been unlocked if we interrupted the kernel.
>>   		 */
>>   		kuap_assert_locked();
>> -
>> -		local_irq_disable();
>>   	}
>> +
>> +	/* irqentry_exit expects to be called with interrupts disabled */
>> +	local_irq_disable();
>>   }
>>   
>>   static inline void arch_interrupt_async_enter_prepare(struct pt_regs *regs)
>> -- 
>> 2.47.3
>>