linux-kernel - Re: [PATCH 1/2] tracing: add support for userspace stacktraces in tracing/iter

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Message-ID: <20081123083740.GD30453@elte.hu>
Date:	Sun, 23 Nov 2008 09:37:40 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Török Edwin <edwintorok@...il.com>
Cc:	srostedt@...hat.com, a.p.zijlstra@...llo.nl, sandmann@...mi.au.dk,
	linux-kernel@...r.kernel.org, viro@...IV.linux.org.uk
Subject: Re: [PATCH 1/2] tracing: add support for userspace stacktraces in
	tracing/iter_ctrl


* Török Edwin <edwintorok@...il.com> wrote:

> +struct stack_frame {
> +     const void __user	*next_fp;
> +     unsigned long           return_address;
> +};

Small detail: please s/return_address/ret_addr - its expressive power 
is the same but as a bonus it will cause less col-80 related 
linebreaks in usage sites.

> +void save_stack_trace_user(struct stack_trace *trace)
> +{
> +	/*
> +	 * Trace user stack if we are not a kernel thread
> +	 */
> +	if (current->mm) {
> +		const struct pt_regs *regs = task_pt_regs(current);
> +		const void __user *fp = (const void __user *)regs->bp;
> +
> +		if (trace->nr_entries < trace->max_entries)
> +			trace->entries[trace->nr_entries++] = regs->ip;
> +
> +		while (trace->nr_entries < trace->max_entries) {
> +			struct stack_frame frame;
> +			frame.next_fp = NULL;

Style: put a newline after variable definitions please.

> +			frame.return_address = 0;
> +			if (!copy_stack_frame(fp, &frame))
> +				break;
> +			if ((unsigned long)fp < regs->sp)
> +				break;
> +			if (frame.return_address)
> +				trace->entries[trace->nr_entries++] =
> +					frame.return_address;

Style: please use curly braces around multi-line conditional 
statements.

> +			if (fp == frame.next_fp)
> +				break;
> +			fp = frame.next_fp;
> +		}
> +	}

Detail: please move the whole "if (current->mm)" into a 
__save_stack_trace_user() helper function - that way it reads cleaner.

> +++ b/include/linux/stacktrace.h
> @@ -18,9 +18,17 @@ extern void save_stack_trace_tsk(struct task_struct *tsk,
>  				struct stack_trace *trace);
>  
>  extern void print_stack_trace(struct stack_trace *trace, int spaces);
> +
> +#ifdef CONFIG_X86
> +extern void save_stack_trace_user(struct stack_trace *trace);
> +#else
> +# define save_stack_trace_user(trace)              do { } while (0)
> +#endif

Bug: this should not be CONFIG_X86. Please introduce (in a separate 
patch from other cleanups) a CONFIG_USER_STACKTRACE_SUPPORT in 
arch/x86/Kconfig and use that instead.

> +
>  #else
>  # define save_stack_trace(trace)			do { } while (0)
>  # define save_stack_trace_tsk(tsk, trace)		do { } while (0)
> +# define save_stack_trace_user(trace)              do { } while (0)

Style: these should be tabs, not spaces ^^^^^^^^^^^^

> +static void ftrace_trace_userstack(struct trace_array *tr,
> +		   struct trace_array_cpu *data,
> +		   unsigned long flags, int pc)
> +{
> +	struct userstack_entry *entry;
> +	struct stack_trace trace;
> +	struct ring_buffer_event *event;
> +	unsigned long irq_flags;

Detail: please use the customary ftrace variable definitions style:

> +	struct ring_buffer_event *event;
> +	struct userstack_entry *entry;
> +	struct stack_trace trace;
> +	unsigned long irq_flags;

note how it's ordered by line length.

> +static int
> +seq_print_userip_objs(const struct userstack_entry *entry, struct trace_seq *s,
> +		unsigned long sym_flags)
> +{
> +	int ret = 1;
> +	unsigned i;

Detail: please use "unsigned int" so that we have less type patterns 
to look for.

> +
> +	for (i = 0; i < FTRACE_STACK_ENTRIES; i++) {
> +		unsigned long ip = entry->caller[i];
> +
> +		if (ip == ULONG_MAX || !ret)
> +			break;
> +		if (i)
> +			ret = trace_seq_puts(s, " <- ");
> +		if (!ip) {
> +			ret = trace_seq_puts(s, "??");
> +			continue;
> +		}
> +		if (ret /*&& (sym_flags & TRACE_ITER_SYM_ADDR)*/)
> +			ret = trace_seq_printf(s, " <" IP_FMT ">", ip);

Detail: do we need that commented-out condition?

	Ingo
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