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 <[email protected]>
> Closes:
> https://lore.kernel.org/all/[email protected]/
> Signed-off-by: Shrikanth Hegde <[email protected]>
> ---
>
> 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
>
