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 <redacted>
Closes: https://lore.kernel.org/all/7904105b-9dfa-4efd-a5ef-bc0276ed255d@linux.ibm.com/ (local)
Signed-off-by: Shrikanth Hegde <redacted>
---

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