Re: [PATCH v2] powerpc/entry: Disable interrupts before irqentry_exit

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

On 03/06/26 6:40 pm, 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.
>
> 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>
> ---

I was able to reproduce this issue consistently, and confirm with this 
patch, reproted issue is fixed. Hence,

Tested-by: Venkat Rao Bagalkote <venkat88@linux.ibm.com>


Regards,

Venkat.


> This applies on top on powerpc/next tree.
> base: 6ed60999d33d '("powerpc: Remove unused functions")'
>
> v1->v2:
> Leave those BUG_ON alone since they are tracking the register
> state of userspace (Peter Zijlstra)
> v1: https://lore.kernel.org/all/20260603095521.198267-1-sshegde@linux.ibm.com/
>
>   arch/powerpc/include/asm/entry-common.h | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/include/asm/entry-common.h b/arch/powerpc/include/asm/entry-common.h
> index de5601282755..fc636c42e89a 100644
> --- a/arch/powerpc/include/asm/entry-common.h
> +++ b/arch/powerpc/include/asm/entry-common.h
> @@ -260,9 +260,10 @@ static inline void arch_interrupt_exit_prepare(struct pt_regs *regs)
>   		 * 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)