[PATCH 2/2] riscv: stacktrace: Make walk_stackframe cross pt_regs frame

guoren
2022-11-09T06:50:25Z

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

The current walk_stackframe with FRAME_POINTER would stop unwinding at
ret_from_exception:
BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1518
in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: init
CPU: 0 PID: 1 Comm: init Not tainted 5.10.113-00021-g15c15974895c-dirty #192
Call Trace:
[<ffffffe0002038c8>] walk_stackframe+0x0/0xee
[<ffffffe000aecf48>] show_stack+0x32/0x4a
[<ffffffe000af1618>] dump_stack_lvl+0x72/0x8e
[<ffffffe000af1648>] dump_stack+0x14/0x1c
[<ffffffe000239ad2>] ___might_sleep+0x12e/0x138
[<ffffffe000239aec>] __might_sleep+0x10/0x18
[<ffffffe000afe3fe>] down_read+0x22/0xa4
[<ffffffe000207588>] do_page_fault+0xb0/0x2fe
[<ffffffe000201b80>] ret_from_exception+0x0/0xc

The optimization would help walk_stackframe cross the pt_regs frame and
get more backtrace of debug info:
BUG: sleeping function called from invalid context at kernel/locking/rwsem.c:1518
in_atomic(): 0, irqs_disabled(): 1, non_block: 0, pid: 1, name: init
CPU: 0 PID: 1 Comm: init Not tainted 5.10.113-00021-g15c15974895c-dirty #192
Call Trace:
[<ffffffe0002038c8>] walk_stackframe+0x0/0xee
[<ffffffe000aecf48>] show_stack+0x32/0x4a
[<ffffffe000af1618>] dump_stack_lvl+0x72/0x8e
[<ffffffe000af1648>] dump_stack+0x14/0x1c
[<ffffffe000239ad2>] ___might_sleep+0x12e/0x138
[<ffffffe000239aec>] __might_sleep+0x10/0x18
[<ffffffe000afe3fe>] down_read+0x22/0xa4
[<ffffffe000207588>] do_page_fault+0xb0/0x2fe
[<ffffffe000201b80>] ret_from_exception+0x0/0xc
[<ffffffe000613c06>] riscv_intc_irq+0x1a/0x72
[<ffffffe000201b80>] ret_from_exception+0x0/0xc
[<ffffffe00033f44a>] vma_link+0x54/0x160
[<ffffffe000341d7a>] mmap_region+0x2cc/0x4d0
[<ffffffe000342256>] do_mmap+0x2d8/0x3ac
[<ffffffe000326318>] vm_mmap_pgoff+0x70/0xb8
[<ffffffe00032638a>] vm_mmap+0x2a/0x36
[<ffffffe0003cfdde>] elf_map+0x72/0x84
[<ffffffe0003d05f8>] load_elf_binary+0x69a/0xec8
[<ffffffe000376240>] bprm_execve+0x246/0x53a
[<ffffffe00037786c>] kernel_execve+0xe8/0x124
[<ffffffe000aecdf2>] run_init_process+0xfa/0x10c
[<ffffffe000aece16>] try_to_run_init_process+0x12/0x3c
[<ffffffe000afa920>] kernel_init+0xb4/0xf8
[<ffffffe000201b80>] ret_from_exception+0x0/0xc

Here is the error injection test code for the above output:
drivers/irqchip/irq-riscv-intc.c:
static asmlinkage void riscv_intc_irq(struct pt_regs *regs)
{
unsigned long cause = regs->cause & ~CAUSE_IRQ_FLAG;
+ u32 tmp; __get_user(tmp, (u32 *)0);

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Cc: Palmer Dabbelt <palmer@rivosinc.com>
Cc: Changbin Du <changbin.du@intel.com>
---
arch/riscv/kernel/entry.S | 2 +-
arch/riscv/kernel/stacktrace.c | 9 +++++++++
2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/kernel/entry.S b/arch/riscv/kernel/entry.S
index b9eda3fcbd6d..329cf51fcd4d 100644
--- a/arch/riscv/kernel/entry.S
+++ b/arch/riscv/kernel/entry.S
@@ -248,7 +248,7 @@ ret_from_syscall_rejected:
andi t0, t0, _TIF_SYSCALL_WORK
bnez t0, handle_syscall_trace_exit

-ret_from_exception:
+ENTRY(ret_from_exception)
REG_L s0, PT_STATUS(sp)
csrc CSR_STATUS, SR_IE
#ifdef CONFIG_TRACE_IRQFLAGS
diff --git a/arch/riscv/kernel/stacktrace.c b/arch/riscv/kernel/stacktrace.c
index bcfe9eb55f80..75c8dd64fc48 100644
--- a/arch/riscv/kernel/stacktrace.c
+++ b/arch/riscv/kernel/stacktrace.c
@@ -16,6 +16,8 @@

#ifdef CONFIG_FRAME_POINTER

+extern asmlinkage void ret_from_exception(void);
+
void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
bool (*fn)(void *, unsigned long), void *arg)
{
@@ -59,6 +61,13 @@ void notrace walk_stackframe(struct task_struct *task, struct pt_regs *regs,
fp = frame->fp;
pc = ftrace_graph_ret_addr(current, NULL, frame->ra,
&frame->ra);
+ if (pc == (unsigned long)ret_from_exception) {
+ if (unlikely(!__kernel_text_address(pc) || !fn(arg, pc)))
+ break;
+
+ pc = ((struct pt_regs *)sp)->epc;
+ fp = ((struct pt_regs *)sp)->s0;
+ }
}

}
--
2.36.1