linux-kernel - Re: [PATCH] powerpc: fix /proc/self/stack

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Date:   Wed, 22 Mar 2017 22:03:53 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Thadeu Lima de Souza Cascardo <cascardo@...onical.com>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH] powerpc: fix /proc/self/stack

Thadeu Lima de Souza Cascardo <cascardo@...onical.com> writes:

> For the current task, the kernel stack would only tell the last time the
> process was rescheduled, if ever. Use the current stack pointer for the
> current task.

You say "fix" in the subject, but is it a bug, or just an enhancement?

> This is also consistent with some other architectures.

Such as .. arm64 and x86 (though it's buried in the unwind code).

> diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
> index 6671195..2446066 100644
> --- a/arch/powerpc/kernel/stacktrace.c
> +++ b/arch/powerpc/kernel/stacktrace.c
> @@ -59,7 +59,12 @@ EXPORT_SYMBOL_GPL(save_stack_trace);
>  
>  void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
>  {
> -	save_context_stack(trace, tsk->thread.ksp, tsk, 0);
> +	unsigned long sp = tsk->thread.ksp;
> +
> +	if (tsk == current)
> +		sp = current_stack_pointer();
	else
		sp = tsk->thread.ksp;

Would be clearer IMHO.

> +
> +	save_context_stack(trace, sp, tsk, 0);
>  }
>  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
>  
> -- 
> 2.9.3


cheers