linux-kernel - Re: [RFC PATCH 2/2] tracing: Teach FETCH_MTD

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Date:	Wed, 27 Nov 2013 20:30:09 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	linux-kernel@...r.kernel.org, Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [RFC PATCH 2/2] tracing: Teach FETCH_MTD_symbol to handle per-cpu
 data

(2013/11/27 2:44), Oleg Nesterov wrote:
> FETCH_FUNC_NAME(symbol) blindly dereferences sc->addr + sc->offset,
> this is not what we want if this symbol is per-cpu. Change this code
> to use this_cpu_ptr(sc->addr) in this case.

This looks good for me :)

Thanks!

> Note: this doesn't work for modules, but module's per-cpu data is
> not visible for kallsyms_lookup_name() anyway.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  kernel/trace/trace_probe.c |   22 ++++++++++++++++++----
>  1 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index 097cc80..a0144b6 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -252,14 +252,28 @@ static struct symbol_cache *alloc_symbol_cache(const char *sym, long offset)
>  	return sc;
>  }
>  
> +static void *sc_calc_addr(struct symbol_cache *sc)
> +{
> +	void *addr = (void*)sc->addr;
> +
> +	if (addr) {
> +		if (addr >= (void *)__per_cpu_start &&
> +		    addr <  (void *)__per_cpu_end)
> +			addr = this_cpu_ptr(addr);
> +
> +		addr += sc->offset;
> +	}
> +
> +	return addr;
> +}
> +
>  #define DEFINE_FETCH_symbol(type)					\
>  static __kprobes void FETCH_FUNC_NAME(symbol, type)(struct pt_regs *regs,\
>  					  void *data, void *dest)	\
>  {									\
> -	struct symbol_cache *sc = data;					\
> -	long off = sc->offset;						\
> -	if (sc->addr)							\
> -		fetch_memory_##type(regs, (void *)sc->addr + off, dest);\
> +	void *addr = sc_calc_addr(data);				\
> +	if (addr)							\
> +		fetch_memory_##type(regs, addr, dest);			\
>  	else								\
>  		*(type *)dest = 0;					\
>  }
> 


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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