LoongArch: Add STACKTRACE support

1. Use common arch_stack_walk() infrastructure to avoid duplicated code
   and avoid taking care of the stack storage and filtering.
2. Add sched_ra (means sched return address) and sched_cfa (means sched
   call frame address) to thread_info, and store them in switch_to().
3. Add __get_wchan() implementation.

Now we can print the process stack and wait channel by cat /proc/*/stack
and /proc/*/wchan.

Signed-off-by: Qing Zhang <zhangqing@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

5 files changed, 70 insertions, 1 deletions

diff --git a/arch/loongarch/kernel/Makefile b/arch/loongarch/kernel/Makefile
index 918600e7b30f..e5be17009fe8 100644
--- a/arch/loongarch/kernel/Makefile
+++ b/arch/loongarch/kernel/Makefile
@@ -15,6 +15,7 @@ obj-$(CONFIG_EFI) 		+= efi.o
 obj-$(CONFIG_CPU_HAS_FPU)	+= fpu.o
 
 obj-$(CONFIG_MODULES)		+= module.o module-sections.o
+obj-$(CONFIG_STACKTRACE)	+= stacktrace.o
 
 obj-$(CONFIG_PROC_FS)		+= proc.o
 
diff --git a/arch/loongarch/kernel/asm-offsets.c b/arch/loongarch/kernel/asm-offsets.c
index 20cd9e16a95a..eb350f3ffae5 100644
--- a/arch/loongarch/kernel/asm-offsets.c
+++ b/arch/loongarch/kernel/asm-offsets.c
@@ -103,6 +103,8 @@ void output_thread_defines(void)
 	OFFSET(THREAD_REG29, task_struct, thread.reg29);
 	OFFSET(THREAD_REG30, task_struct, thread.reg30);
 	OFFSET(THREAD_REG31, task_struct, thread.reg31);
+	OFFSET(THREAD_SCHED_RA, task_struct, thread.sched_ra);
+	OFFSET(THREAD_SCHED_CFA, task_struct, thread.sched_cfa);
 	OFFSET(THREAD_CSRCRMD, task_struct,
 	       thread.csr_crmd);
 	OFFSET(THREAD_CSRPRMD, task_struct,
diff --git a/arch/loongarch/kernel/process.c b/arch/loongarch/kernel/process.c
index 839f0e963152..660492f064e7 100644
--- a/arch/loongarch/kernel/process.c
+++ b/arch/loongarch/kernel/process.c
@@ -135,6 +135,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 	childregs = (struct pt_regs *) childksp - 1;
 	/*  Put the stack after the struct pt_regs.  */
 	childksp = (unsigned long) childregs;
+	p->thread.sched_cfa = 0;
 	p->thread.csr_euen = 0;
 	p->thread.csr_crmd = csr_read32(LOONGARCH_CSR_CRMD);
 	p->thread.csr_prmd = csr_read32(LOONGARCH_CSR_PRMD);
@@ -145,6 +146,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 		p->thread.reg23 = (unsigned long)args->fn;
 		p->thread.reg24 = (unsigned long)args->fn_arg;
 		p->thread.reg01 = (unsigned long)ret_from_kernel_thread;
+		p->thread.sched_ra = (unsigned long)ret_from_kernel_thread;
 		memset(childregs, 0, sizeof(struct pt_regs));
 		childregs->csr_euen = p->thread.csr_euen;
 		childregs->csr_crmd = p->thread.csr_crmd;
@@ -161,6 +163,7 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 	p->thread.reg03 = (unsigned long) childregs;
 	p->thread.reg01 = (unsigned long) ret_from_fork;
+	p->thread.sched_ra = (unsigned long) ret_from_fork;
 
 	/*
 	 * New tasks lose permission to use the fpu. This accelerates context
@@ -181,7 +184,31 @@ int copy_thread(struct task_struct *p, const struct kernel_clone_args *args)
 
 unsigned long __get_wchan(struct task_struct *task)
 {
-	return 0;
+	unsigned long pc;
+	struct unwind_state state;
+
+	if (!try_get_task_stack(task))
+		return 0;
+
+	unwind_start(&state, task, NULL);
+	state.sp = thread_saved_fp(task);
+	get_stack_info(state.sp, state.task, &state.stack_info);
+	state.pc = thread_saved_ra(task);
+#ifdef CONFIG_UNWINDER_PROLOGUE
+	state.type = UNWINDER_PROLOGUE;
+#endif
+	for (; !unwind_done(&state); unwind_next_frame(&state)) {
+		pc = unwind_get_return_address(&state);
+		if (!pc)
+			break;
+		if (in_sched_functions(pc))
+			continue;
+		break;
+	}
+
+	put_task_stack(task);
+
+	return pc;
 }
 
 bool in_irq_stack(unsigned long stack, struct stack_info *info)
diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c
new file mode 100644
index 000000000000..e690c1c769f2
--- /dev/null
+++ b/arch/loongarch/kernel/stacktrace.c
@@ -0,0 +1,37 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Stack trace management functions
+ *
+ * Copyright (C) 2022 Loongson Technology Corporation Limited
+ */
+#include <linux/sched.h>
+#include <linux/stacktrace.h>
+
+#include <asm/stacktrace.h>
+#include <asm/unwind.h>
+
+void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie,
+		     struct task_struct *task, struct pt_regs *regs)
+{
+	unsigned long addr;
+	struct pt_regs dummyregs;
+	struct unwind_state state;
+
+	regs = &dummyregs;
+
+	if (task == current) {
+		regs->regs[3] = (unsigned long)__builtin_frame_address(0);
+		regs->csr_era = (unsigned long)__builtin_return_address(0);
+	} else {
+		regs->regs[3] = thread_saved_fp(task);
+		regs->csr_era = thread_saved_ra(task);
+	}
+
+	regs->regs[1] = 0;
+	for (unwind_start(&state, task, regs);
+	      !unwind_done(&state); unwind_next_frame(&state)) {
+		addr = unwind_get_return_address(&state);
+		if (!addr || !consume_entry(cookie, addr))
+			break;
+	}
+}
diff --git a/arch/loongarch/kernel/switch.S b/arch/loongarch/kernel/switch.S
index 37e84ac8ffc2..43ebbc3990f7 100644
--- a/arch/loongarch/kernel/switch.S
+++ b/arch/loongarch/kernel/switch.S
@@ -21,6 +21,8 @@ SYM_FUNC_START(__switch_to)
 
 	cpu_save_nonscratch a0
 	stptr.d	ra, a0, THREAD_REG01
+	stptr.d a3, a0, THREAD_SCHED_RA
+	stptr.d a4, a0, THREAD_SCHED_CFA
 	move	tp, a2
 	cpu_restore_nonscratch a1