Re: [patch added to 3.12-stable] tracing: Fix check for cpu online when event is disabled

[Luis Henriques <luis.henriques@canonical.com>]

On Mon, Mar 14, 2016 at 02:16:44PM +0100, Jiri Slaby wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
> 
> This patch has been added to the 3.12 stable tree. If you have any
> objections, please let us know.
>

Please note that this patch was tagged for stable 3.18+.

Cheers,
--
Lu�s

> ===============
> 
> commit dc17147de328a74bbdee67c1bf37d2f1992de756 upstream.
> 
> Commit f37755490fe9b ("tracepoints: Do not trace when cpu is offline") added
> a check to make sure that tracepoints only get called when the cpu is
> online, as it uses rcu_read_lock_sched() for protection.
> 
> Commit 3a630178fd5f3 ("tracing: generate RCU warnings even when tracepoints
> are disabled") added lockdep checks (including rcu checks) for events that
> are not enabled to catch possible RCU issues that would only be triggered if
> a trace event was enabled. Commit f37755490fe9b only stopped the warnings
> when the trace event was enabled but did not prevent warnings if the trace
> event was called when disabled.
> 
> To fix this, the cpu online check is moved to where the condition is added
> to the trace event. This will place the cpu online check in all places that
> it may be used now and in the future.
> 
> Fixes: f37755490fe9b ("tracepoints: Do not trace when cpu is offline")
> Fixes: 3a630178fd5f3 ("tracing: generate RCU warnings even when tracepoints are disabled")
> Reported-by: Sudeep Holla <sudeep.holla@arm.com>
> Tested-by: Sudeep Holla <sudeep.holla@arm.com>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  include/linux/tracepoint.h | 17 +++++++++--------
>  1 file changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/tracepoint.h b/include/linux/tracepoint.h
> index c1248996006f..9ff9ca22cfb7 100644
> --- a/include/linux/tracepoint.h
> +++ b/include/linux/tracepoint.h
> @@ -129,9 +129,6 @@ static inline void tracepoint_synchronize_unregister(void)
>  		void *it_func;						\
>  		void *__data;						\
>  									\
> -		if (!cpu_online(raw_smp_processor_id()))		\
> -			return;						\
> -									\
>  		if (!(cond))						\
>  			return;						\
>  		prercu;							\
> @@ -265,15 +262,19 @@ static inline void tracepoint_synchronize_unregister(void)
>   * "void *__data, proto" as the callback prototype.
>   */
>  #define DECLARE_TRACE_NOARGS(name)					\
> -		__DECLARE_TRACE(name, void, , 1, void *__data, __data)
> +	__DECLARE_TRACE(name, void, ,					\
> +			cpu_online(raw_smp_processor_id()),		\
> +			void *__data, __data)
>  
>  #define DECLARE_TRACE(name, proto, args)				\
> -		__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), 1,	\
> -				PARAMS(void *__data, proto),		\
> -				PARAMS(__data, args))
> +	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
> +			cpu_online(raw_smp_processor_id()),		\
> +			PARAMS(void *__data, proto),			\
> +			PARAMS(__data, args))
>  
>  #define DECLARE_TRACE_CONDITION(name, proto, args, cond)		\
> -	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args), PARAMS(cond), \
> +	__DECLARE_TRACE(name, PARAMS(proto), PARAMS(args),		\
> +			cpu_online(raw_smp_processor_id()) && (PARAMS(cond)), \
>  			PARAMS(void *__data, proto),			\
>  			PARAMS(__data, args))
>  
> -- 
> 2.7.3
> 
> --
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