arm64: let the core code deal with preempt_count
Commit f27dde8deef3 (sched: Add NEED_RESCHED to the preempt_count)
introduced the use of bit 31 in preempt_count for obscure scheduling
purposes.
This causes interrupts taken from EL0 to hit the (open coded) BUG when
this flag is flipped while handling the interrupt (we compare the
values before and after, and kill the kernel if they are different).
The fix is to stop messing with the preempt count entirely, as this
is already being dealt with in the generic code (irq_enter/irq_exit).
Tested on a dual A53 FPGA running cyclictest.
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index e116614..4d2c6f3 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -309,15 +309,12 @@
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif
+
+ irq_handler
+
#ifdef CONFIG_PREEMPT
get_thread_info tsk
- ldr w24, [tsk, #TI_PREEMPT] // get preempt count
- add w0, w24, #1 // increment it
- str w0, [tsk, #TI_PREEMPT]
-#endif
- irq_handler
-#ifdef CONFIG_PREEMPT
- str w24, [tsk, #TI_PREEMPT] // restore preempt count
+ ldr w24, [tsk, #TI_PREEMPT] // restore preempt count
cbnz w24, 1f // preempt count != 0
ldr x0, [tsk, #TI_FLAGS] // get flags
tbz x0, #TIF_NEED_RESCHED, 1f // needs rescheduling?
@@ -507,22 +504,10 @@
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_off
#endif
- get_thread_info tsk
-#ifdef CONFIG_PREEMPT
- ldr w24, [tsk, #TI_PREEMPT] // get preempt count
- add w23, w24, #1 // increment it
- str w23, [tsk, #TI_PREEMPT]
-#endif
+
irq_handler
-#ifdef CONFIG_PREEMPT
- ldr w0, [tsk, #TI_PREEMPT]
- str w24, [tsk, #TI_PREEMPT]
- cmp w0, w23
- b.eq 1f
- mov x1, #0
- str x1, [x1] // BUG
-1:
-#endif
+ get_thread_info tsk
+
#ifdef CONFIG_TRACE_IRQFLAGS
bl trace_hardirqs_on
#endif