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

[Guo Ren]

On Wed, Nov 9, 2022 at 2:50 PM <guoren@xxxxxxxxxx> wrote:
>
> From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
> Cc: Changbin Du <changbin.du@xxxxxxxxx>
> ---
>  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) {
I forgot ret_from_syscall because I tested it on the generic_entry
series base. I would merge this patch into the generic_entry series as
an optimization.

> +                               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
>


-- 
Best Regards
 Guo Ren