5.7-rc interrupt_return Unrecoverable exception 380

[Hugh Dickins <hughd@google.com>]

Hi Nick,

I've been getting an "Unrecoverable exception 380" after a few hours
of load on the G5 (yes, that G5!) with 5.7-rc: when interrupt_return
checks lazy_irq_pending, it crashes at check_preemption_disabled+0x24
with CONFIG_DEBUG_PREEMPT=y.

check_preemption_disabled():
lib/smp_processor_id.c:13
   0:	7c 08 02 a6 	mflr    r0
   4:	fb e1 ff f8 	std     r31,-8(r1)
   8:	fb 61 ff d8 	std     r27,-40(r1)
   c:	fb 81 ff e0 	std     r28,-32(r1)
  10:	fb a1 ff e8 	std     r29,-24(r1)
  14:	fb c1 ff f0 	std     r30,-16(r1)
get_current():
arch/powerpc/include/asm/current.h:20
  18:	eb ed 01 88 	ld      r31,392(r13)
check_preemption_disabled():
lib/smp_processor_id.c:13
  1c:	f8 01 00 10 	std     r0,16(r1)
  20:	f8 21 ff 61 	stdu    r1,-160(r1)
__read_once_size():
include/linux/compiler.h:199
  24:	81 3f 00 00 	lwz     r9,0(r31)
check_preemption_disabled():
lib/smp_processor_id.c:14
  28:	a3 cd 00 02 	lhz     r30,2(r13)

I don't read ppc assembly, and have not jotted down the registers,
but hope you can make sense of it. I get around it with the patch
below (just avoiding the debug), but have no idea whether it's a
necessary fix or a hacky workaround.

Hugh

--- 5.7-rc3/arch/powerpc/include/asm/hw_irq.h	2020-04-12 16:24:29.802769727 -0700
+++ linux/arch/powerpc/include/asm/hw_irq.h	2020-04-27 11:31:10.000000000 -0700
@@ -252,7 +252,7 @@ static inline bool arch_irqs_disabled(vo
 
 static inline bool lazy_irq_pending(void)
 {
-	return !!(get_paca()->irq_happened & ~PACA_IRQ_HARD_DIS);
+	return !!(local_paca->irq_happened & ~PACA_IRQ_HARD_DIS);
 }
 
 /*