Re: [PATCH 7/7] arch: Fix STACKTRACE_SUPPORT

[Guo Ren]

Thx Peter,

On Fri, Oct 8, 2021 at 7:18 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
>
> A few archs got save_stack_trace_tsk() vs in_sched_functions() wrong.
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>  arch/csky/kernel/stacktrace.c  |    7 ++++++-
>  arch/mips/kernel/stacktrace.c  |   27 ++++++++++++++++-----------
>  arch/nds32/kernel/stacktrace.c |   21 +++++++++++----------
>  3 files changed, 33 insertions(+), 22 deletions(-)
>
> --- a/arch/csky/kernel/stacktrace.c
> +++ b/arch/csky/kernel/stacktrace.c
> @@ -122,12 +122,17 @@ static bool save_trace(unsigned long pc,
>         return __save_trace(pc, arg, false);
>  }
>
> +static bool save_trace_nosched(unsigned long pc, void *arg)
> +{
> +       return __save_trace(pc, arg, true);
> +}
> +
>  /*
>   * Save stack-backtrace addresses into a stack_trace buffer.
>   */
>  void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
>  {
> -       walk_stackframe(tsk, NULL, save_trace, trace);
> +       walk_stackframe(tsk, NULL, save_trace_nosched, trace);
>  }
>  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
I think the patch should be:
@@ -138,7 +138,7 @@ static bool __save_trace(unsigned long pc, void
*arg, bool nosched)

 static bool save_trace(unsigned long pc, void *arg)
 {
-       return __save_trace(pc, arg, false);
+       return __save_trace(pc, arg, true);
 }

Another question:
If we put sched_text in the backtrace buffer, just cause put no useful
information in wchan, right?
(I think it wouldn't cause a worse problem than debugging.)


>
> --- a/arch/mips/kernel/stacktrace.c
> +++ b/arch/mips/kernel/stacktrace.c
> @@ -66,16 +66,7 @@ static void save_context_stack(struct st
>  #endif
>  }
>
> -/*
> - * Save stack-backtrace addresses into a stack_trace buffer.
> - */
> -void save_stack_trace(struct stack_trace *trace)
> -{
> -       save_stack_trace_tsk(current, trace);
> -}
> -EXPORT_SYMBOL_GPL(save_stack_trace);
> -
> -void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +static void __save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace, bool savesched)
>  {
>         struct pt_regs dummyregs;
>         struct pt_regs *regs = &dummyregs;
> @@ -88,6 +79,20 @@ void save_stack_trace_tsk(struct task_st
>                 regs->cp0_epc = tsk->thread.reg31;
>         } else
>                 prepare_frametrace(regs);
> -       save_context_stack(trace, tsk, regs, tsk == current);
> +       save_context_stack(trace, tsk, regs, savesched);
> +}
> +
> +/*
> + * Save stack-backtrace addresses into a stack_trace buffer.
> + */
> +void save_stack_trace(struct stack_trace *trace)
> +{
> +       __save_stack_trace_tsk(current, trace, true);
> +}
> +EXPORT_SYMBOL_GPL(save_stack_trace);
> +
> +void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +{
> +       __save_stack_trace_tsk(tsk, trace, false);
>  }
>  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
> --- a/arch/nds32/kernel/stacktrace.c
> +++ b/arch/nds32/kernel/stacktrace.c
> @@ -6,25 +6,16 @@
>  #include <linux/stacktrace.h>
>  #include <linux/ftrace.h>
>
> -void save_stack_trace(struct stack_trace *trace)
> -{
> -       save_stack_trace_tsk(current, trace);
> -}
> -EXPORT_SYMBOL_GPL(save_stack_trace);
> -
> -void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +static void __save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace, bool savesched)
>  {
>         unsigned long *fpn;
>         int skip = trace->skip;
> -       int savesched;
>         int graph_idx = 0;
>
>         if (tsk == current) {
>                 __asm__ __volatile__("\tori\t%0, $fp, #0\n":"=r"(fpn));
> -               savesched = 1;
>         } else {
>                 fpn = (unsigned long *)thread_saved_fp(tsk);
> -               savesched = 0;
>         }
>
>         while (!kstack_end(fpn) && !((unsigned long)fpn & 0x3)
> @@ -50,4 +41,14 @@ void save_stack_trace_tsk(struct task_st
>                 fpn = (unsigned long *)fpp;
>         }
>  }
> +void save_stack_trace(struct stack_trace *trace)
> +{
> +       __save_stack_trace_tsk(current, trace, true);
> +}
> +EXPORT_SYMBOL_GPL(save_stack_trace);
> +
> +void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
> +{
> +       __save_stack_trace_tsk(tsk, trace, false);
> +}
>  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
>
>


--
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/