Re: [PATCH] powerpc/entry: Use hard_irq_disable() in arch_interrupt_exit_prepare()
From: Shrikanth Hegde <hidden>
Date: 2026-08-14 05:37:08
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On 8/12/26 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.This is good explanation, but what i not understanding is, why pattern of setting PACA_IRQ_HARD_DIS changed? Previous code at interrupt_exit_kernel_prepare which did local_irq_disable too. Please check where was PACA_IRQ_HARD_DIS set without GENERIC_ENTRY which was preventing this from happening?
quoted hunk ↗ jump to hunk
Fixes: 334f3f6d7a16 ("powerpc/entry: Disable interrupts before irqentry_exit") Reported-by: Venkat Rao Bagalkote <redacted> Closes: https://lore.kernel.org/all/6f9bfb0f-b14c-468e-bb9f-c157d120d0dc@linux.ibm.com/ (local) Signed-off-by: Mukesh Kumar Chaurasiya (IBM) <redacted> --- 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)