linux-kernel - Re: [PATCH] s390:ftrace: add save_stack_trace

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Date:	Mon, 1 Feb 2016 10:00:11 +0100
From:	Heiko Carstens <heiko.carstens@...ibm.com>
To:	Pratyush Anand <panand@...hat.com>
Cc:	schwidefsky@...ibm.com, rostedt@...dmis.org,
	linux-s390@...r.kernel.org, Chunyu Hu <chuhu@...hat.com>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] s390:ftrace: add save_stack_trace_regs()

On Fri, Jan 29, 2016 at 10:50:28AM +0530, Pratyush Anand wrote:
> Implement save_stack_trace_regs, so that stacktrace of a kprobe events can
> be obtained.
> 
> Without this we see following warning:
> "save_stack_trace_regs() not implemented yet."
> when we execute:
> echo stacktrace > /sys/kernel/debug/tracing/trace_options
> echo "p kfree" >> /sys/kernel/debug/tracing/kprobe_events
> echo 1 > /sys/kernel/debug/tracing/events/kprobes/enable
> 
> Reported-by: Chunyu Hu <chuhu@...hat.com>
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> ---
>  arch/s390/kernel/stacktrace.c | 13 +++++++++++++
>  1 file changed, 13 insertions(+)
> 
> diff --git a/arch/s390/kernel/stacktrace.c b/arch/s390/kernel/stacktrace.c
> index 1785cd82253c..586da400f931 100644
> --- a/arch/s390/kernel/stacktrace.c
> +++ b/arch/s390/kernel/stacktrace.c
> @@ -94,3 +94,16 @@ void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
>  		trace->entries[trace->nr_entries++] = ULONG_MAX;
>  }
>  EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
> +
> +void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
> +{
> +	unsigned long sp, low, high;
> +
> +	sp = kernel_stack_pointer(regs);
> +	low = (unsigned long) task_stack_page(current);
> +	high = (unsigned long) task_pt_regs(current);
> +	save_context_stack(trace, sp, low, high, 0);
> +	if (trace->nr_entries < trace->max_entries)
> +		trace->entries[trace->nr_entries++] = ULONG_MAX;
> +}
> +EXPORT_SYMBOL_GPL(save_stack_trace_regs);

While playing around with this, I discovered a couple of bugs in our
stacktrace code. However this patch is also not correct, since it will save
a stacktrace only if being called in process context, but not for interrupt
context.
I will fix this within this patch.