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

[Palmer Dabbelt]

On Tue, 08 Nov 2022 22:49:37 PST (-0800), guoren at kernel.org wrote:
> From: Guo Ren <guoren at 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 at linux.alibaba.com>
> Signed-off-by: Guo Ren <guoren at kernel.org>
> Cc: Palmer Dabbelt <palmer at rivosinc.com>
> Cc: Changbin Du <changbin.du at 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)

This at least needs an END(), but it should also be converted over to 
some non-function entry flavor.  I converted it over to 
SYM_CODE_START_NOALIGN(), with the cooresponding SYM_CODE_END(), and put 
it on for-next.

>  	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;
> +			}
>  		}
>
>  	}