arm64: Add do_softirq_own_stack() and enable irq_stacks

entry.S is modified to switch to the per_cpu irq_stack during el{0,1}_irq.
irq_count is used to detect recursive interrupts on the irq_stack, it is
updated late by do_softirq_own_stack(), when called on the irq_stack, before
__do_softirq() re-enables interrupts to process softirqs.

do_softirq_own_stack() is added by this patch, but does not yet switch
stack.

This patch adds the dummy stack frame and data needed by the previous
stack tracing patches.

Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

1 files changed, 37 insertions, 1 deletions

diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
index 1e3cef578e21..ff7ebb710e51 100644
--- a/arch/arm64/kernel/irq.c
+++ b/arch/arm64/kernel/irq.c
@@ -25,14 +25,24 @@
 #include <linux/irq.h>
 #include <linux/smp.h>
 #include <linux/init.h>
+#include <linux/interrupt.h>
 #include <linux/irqchip.h>
 #include <linux/seq_file.h>
 
 unsigned long irq_err_count;
 
-/* irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned */
+/*
+ * irq stack only needs to be 16 byte aligned - not IRQ_STACK_SIZE aligned.
+ * irq_stack[0] is used as irq_count, a non-zero value indicates the stack
+ * is in use, and el?_irq() shouldn't switch to it. This is used to detect
+ * recursive use of the irq_stack, it is lazily updated by
+ * do_softirq_own_stack(), which is called on the irq_stack, before
+ * re-enabling interrupts to process softirqs.
+ */
 DEFINE_PER_CPU(unsigned long [IRQ_STACK_SIZE/sizeof(long)], irq_stack) __aligned(16);
 
+#define IRQ_COUNT()	(*per_cpu(irq_stack, smp_processor_id()))
+
 int arch_show_interrupts(struct seq_file *p, int prec)
 {
 	show_ipi_list(p, prec);
@@ -56,3 +66,29 @@ void __init init_IRQ(void)
 	if (!handle_arch_irq)
 		panic("No interrupt controller found.");
 }
+
+/*
+ * do_softirq_own_stack() is called from irq_exit() before __do_softirq()
+ * re-enables interrupts, at which point we may re-enter el?_irq(). We
+ * increase irq_count here so that el1_irq() knows that it is already on the
+ * irq stack.
+ *
+ * Called with interrupts disabled, so we don't worry about moving cpu, or
+ * being interrupted while modifying irq_count.
+ *
+ * This function doesn't actually switch stack.
+ */
+void do_softirq_own_stack(void)
+{
+	int cpu = smp_processor_id();
+
+	WARN_ON_ONCE(!irqs_disabled());
+
+	if (on_irq_stack(current_stack_pointer, cpu)) {
+		IRQ_COUNT()++;
+		__do_softirq();
+		IRQ_COUNT()--;
+	} else {
+		__do_softirq();
+	}
+}