[RFC PATCH 1/2] arm64: run softirqs on the per-CPU IRQ stack

[Qi Zheng]

Currently arm64 supports per-CPU IRQ stack, but softirqs
are still handled in the task context.

Since any call to local_bh_enable() at any level in the task's
call stack may trigger a softirq processing run, which could
potentially cause a task stack overflow if the combined stack
footprints exceed the stack's size, let's run these softirqs
on the IRQ stack as well.

Signed-off-by: Qi Zheng <zhengqi.arch at bytedance.com>
---
 arch/arm64/Kconfig      |  1 +
 arch/arm64/kernel/irq.c | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 3491d0d99891..402e16fec02a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -230,6 +230,7 @@ config ARM64
 	select HAVE_ARCH_USERFAULTFD_MINOR if USERFAULTFD
 	select TRACE_IRQFLAGS_SUPPORT
 	select TRACE_IRQFLAGS_NMI_SUPPORT
+	select HAVE_SOFTIRQ_ON_OWN_STACK
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
index bda49430c9ea..e6aa37672fd4 100644
--- a/arch/arm64/kernel/irq.c
+++ b/arch/arm64/kernel/irq.c
@@ -22,6 +22,7 @@
 #include <linux/vmalloc.h>
 #include <asm/daifflags.h>
 #include <asm/vmap_stack.h>
+#include <asm/exception.h>
 
 /* Only access this in an NMI enter/exit */
 DEFINE_PER_CPU(struct nmi_ctx, nmi_contexts);
@@ -71,6 +72,16 @@ static void init_irq_stacks(void)
 }
 #endif
 
+static void ____do_softirq(struct pt_regs *regs)
+{
+	__do_softirq();
+}
+
+void do_softirq_own_stack(void)
+{
+	call_on_irq_stack(NULL, ____do_softirq);
+}
+
 static void default_handle_irq(struct pt_regs *regs)
 {
 	panic("IRQ taken without a root IRQ handler\n");
-- 
2.20.1