[PATCH V4 7/8] riscv: Support HAVE_SOFTIRQ_ON_OWN_STACK

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

Add the HAVE_SOFTIRQ_ON_OWN_STACK feature for the IRQ_STACKS config. The
irq and softirq use the same independent irq_stack of percpu by time
division multiplexing.

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
---
 arch/riscv/Kconfig      |  7 ++++---
 arch/riscv/kernel/irq.c | 16 ++++++++++++++++
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a8a12b4ba1a9..da548ed7d107 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -434,12 +434,13 @@ config FPU
 	  If you don't know what to do here, say Y.
 
 config IRQ_STACKS
-	bool "Independent irq stacks"
+	bool "Independent irq & softirq stacks"
 	default y
 	select HAVE_IRQ_EXIT_ON_IRQ_STACK
+	select HAVE_SOFTIRQ_ON_OWN_STACK
 	help
-	  Add independent irq stacks for percpu to prevent kernel stack overflows.
-	  We may save some memory footprint by disabling IRQ_STACKS.
+	  Add independent irq & softirq stacks for percpu to prevent kernel stack
+	  overflows. We may save some memory footprint by disabling IRQ_STACKS.
 
 endmenu # "Platform type"
 
diff --git a/arch/riscv/kernel/irq.c b/arch/riscv/kernel/irq.c
index 5ad4952203c5..c09cd4d28308 100644
--- a/arch/riscv/kernel/irq.c
+++ b/arch/riscv/kernel/irq.c
@@ -11,6 +11,7 @@
 #include <linux/seq_file.h>
 #include <asm/smp.h>
 #include <asm/vmap_stack.h>
+#include <asm/softirq_stack.h>
 
 #ifdef CONFIG_IRQ_STACKS
 static DEFINE_PER_CPU(ulong *, irq_stack_ptr);
@@ -38,6 +39,21 @@ static void init_irq_stacks(void)
 		per_cpu(irq_stack_ptr, cpu) = per_cpu(irq_stack, cpu);
 }
 #endif /* CONFIG_VMAP_STACK */
+
+#ifndef CONFIG_PREEMPT_RT
+static void do_riscv_softirq(struct pt_regs *regs)
+{
+	__do_softirq();
+}
+
+void do_softirq_own_stack(void)
+{
+	ulong *sp = per_cpu(irq_stack_ptr, smp_processor_id());
+
+	call_on_stack(NULL, sp, do_riscv_softirq, 0);
+}
+#endif /* CONFIG_PREEMPT_RT */
+
 #else
 static void init_irq_stacks(void) {}
 #endif /* CONFIG_IRQ_STACKS */
-- 
2.36.1