kernel: backport MIPS changes introducing a separate IRQ stack

Prevents crashes when IRQs arrive when the current kernel stack context
already contains deeply nested function calls, e.g. when stacking lots
of network devices on top of each other

Signed-off-by: Felix Fietkau <nbd@nbd.name>

1 files changed, 42 insertions, 0 deletions

diff --git a/target/linux/generic/patches-4.4/062-02-MIPS-Stack-unwinding-while-on-IRQ-stack.patch b/target/linux/generic/patches-4.4/062-02-MIPS-Stack-unwinding-while-on-IRQ-stack.patch
new file mode 100644
index 0000000000..513e904e52
--- /dev/null
+++ b/target/linux/generic/patches-4.4/062-02-MIPS-Stack-unwinding-while-on-IRQ-stack.patch
@@ -0,0 +1,42 @@
+From: Matt Redfearn <matt.redfearn@imgtec.com>
+Date: Mon, 19 Dec 2016 14:20:57 +0000
+Subject: [PATCH] MIPS: Stack unwinding while on IRQ stack
+
+Within unwind stack, check if the stack pointer being unwound is within
+the CPU's irq_stack and if so use that page rather than the task's stack
+page.
+
+Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
+---
+
+--- a/arch/mips/kernel/process.c
++++ b/arch/mips/kernel/process.c
+@@ -32,6 +32,7 @@
+ #include <asm/cpu.h>
+ #include <asm/dsp.h>
+ #include <asm/fpu.h>
++#include <asm/irq.h>
+ #include <asm/msa.h>
+ #include <asm/pgtable.h>
+ #include <asm/mipsregs.h>
+@@ -507,7 +508,19 @@ EXPORT_SYMBOL(unwind_stack_by_address);
+ unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
+ 			   unsigned long pc, unsigned long *ra)
+ {
+-	unsigned long stack_page = (unsigned long)task_stack_page(task);
++	unsigned long stack_page = 0;
++	int cpu;
++
++	for_each_possible_cpu(cpu) {
++		if (on_irq_stack(cpu, *sp)) {
++			stack_page = (unsigned long)irq_stack[cpu];
++			break;
++		}
++	}
++
++	if (!stack_page)
++		stack_page = (unsigned long)task_stack_page(task);
++
+ 	return unwind_stack_by_address(stack_page, sp, pc, ra);
+ }
+ #endif