linux-kernel - Re: [tip:tracing/urgent] tracing: Remove side effect from module tracepoints that caused a GPF

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Date:	Sat, 27 Mar 2010 00:10:26 -0400
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Steven Rostedt <rostedt@...dmis.org>, mingo@...hat.com,
	hpa@...or.com, linux-kernel@...r.kernel.org, lizf@...fujitsu.com,
	tglx@...utronix.de, randy.dunlap@...cle.com
Cc:	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:tracing/urgent] tracing: Remove side effect from module
	tracepoints that caused a GPF

Steven, how about also merging my patch that address the underlying bug in
module.h that cause the GPF in the first place into 2.6.33.x ?

Thanks,

Mathieu

* tip-bot for Li Zefan (lizf@...fujitsu.com) wrote:
> Commit-ID:  3656d5431262ca25aba01d08a5b6e1295ab8feeb
> Gitweb:     http://git.kernel.org/tip/3656d5431262ca25aba01d08a5b6e1295ab8feeb
> Author:     Li Zefan <lizf@...fujitsu.com>
> AuthorDate: Wed, 24 Mar 2010 10:57:43 +0800
> Committer:  Steven Rostedt <rostedt@...dmis.org>
> CommitDate: Fri, 26 Mar 2010 15:30:21 -0400
> 
> tracing: Remove side effect from module tracepoints that caused a GPF
> 
> Remove the @refcnt argument, because it has side-effects, and arguments with
> side-effects are not skipped by the jump over disabled instrumentation and are
> executed even when the tracepoint is disabled.
> 
> This was also causing a GPF as found by Randy Dunlap:
> 
> Subject: 2.6.33 GP fault only when built with tracing
> LKML-Reference: <4BA2B69D.3000309@...cle.com>
> 
> Tested-by: Randy Dunlap <randy.dunlap@...cle.com>
> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
> Cc: stable@...nel.org
> Signed-off-by: Li Zefan <lizf@...fujitsu.com>
> LKML-Reference: <4BA97FA7.6040406@...fujitsu.com>
> Signed-off-by: Steven Rostedt <rostedt@...dmis.org>
> ---
>  include/linux/module.h        |    6 ++----
>  include/trace/events/module.h |   14 +++++++-------
>  kernel/module.c               |    3 +--
>  3 files changed, 10 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/module.h b/include/linux/module.h
> index 5e869ff..393ec39 100644
> --- a/include/linux/module.h
> +++ b/include/linux/module.h
> @@ -460,8 +460,7 @@ static inline void __module_get(struct module *module)
>  	if (module) {
>  		preempt_disable();
>  		__this_cpu_inc(module->refptr->count);
> -		trace_module_get(module, _THIS_IP_,
> -				 __this_cpu_read(module->refptr->count));
> +		trace_module_get(module, _THIS_IP_);
>  		preempt_enable();
>  	}
>  }
> @@ -475,8 +474,7 @@ static inline int try_module_get(struct module *module)
>  
>  		if (likely(module_is_live(module))) {
>  			__this_cpu_inc(module->refptr->count);
> -			trace_module_get(module, _THIS_IP_,
> -				__this_cpu_read(module->refptr->count));
> +			trace_module_get(module, _THIS_IP_);
>  		}
>  		else
>  			ret = 0;
> diff --git a/include/trace/events/module.h b/include/trace/events/module.h
> index 4b0f48b..a585f81 100644
> --- a/include/trace/events/module.h
> +++ b/include/trace/events/module.h
> @@ -53,9 +53,9 @@ TRACE_EVENT(module_free,
>  
>  DECLARE_EVENT_CLASS(module_refcnt,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt),
> +	TP_ARGS(mod, ip),
>  
>  	TP_STRUCT__entry(
>  		__field(	unsigned long,	ip		)
> @@ -65,7 +65,7 @@ DECLARE_EVENT_CLASS(module_refcnt,
>  
>  	TP_fast_assign(
>  		__entry->ip	= ip;
> -		__entry->refcnt	= refcnt;
> +		__entry->refcnt	= __this_cpu_read(mod->refptr->count);
>  		__assign_str(name, mod->name);
>  	),
>  
> @@ -75,16 +75,16 @@ DECLARE_EVENT_CLASS(module_refcnt,
>  
>  DEFINE_EVENT(module_refcnt, module_get,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt)
> +	TP_ARGS(mod, ip)
>  );
>  
>  DEFINE_EVENT(module_refcnt, module_put,
>  
> -	TP_PROTO(struct module *mod, unsigned long ip, int refcnt),
> +	TP_PROTO(struct module *mod, unsigned long ip),
>  
> -	TP_ARGS(mod, ip, refcnt)
> +	TP_ARGS(mod, ip)
>  );
>  
>  TRACE_EVENT(module_request,
> diff --git a/kernel/module.c b/kernel/module.c
> index c968d36..21591ad 100644
> --- a/kernel/module.c
> +++ b/kernel/module.c
> @@ -800,8 +800,7 @@ void module_put(struct module *module)
>  		preempt_disable();
>  		__this_cpu_dec(module->refptr->count);
>  
> -		trace_module_put(module, _RET_IP_,
> -				 __this_cpu_read(module->refptr->count));
> +		trace_module_put(module, _RET_IP_);
>  		/* Maybe they're waiting for us to drop reference? */
>  		if (unlikely(!module_is_live(module)))
>  			wake_up_process(module->waiter);

-- 
Mathieu Desnoyers
Operating System Efficiency R&D Consultant
EfficiOS Inc.
http://www.efficios.com
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