linux-kernel - Re: [RFC][PATCH 01/10] tracing: Do not reference event data in post call triggers

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Message-Id: <20180512210438.f876501a1c7f2f5623f9e336@kernel.org>
Date:   Sat, 12 May 2018 21:04:38 +0900
From:   Masami Hiramatsu <mhiramat@...nel.org>
To:     Steven Rostedt <rostedt@...dmis.org>
Cc:     linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tom Zanussi <tom.zanussi@...ux.intel.com>,
        Clark Williams <williams@...hat.com>,
        Karim Yaghmour <karim.yaghmour@...rsys.com>,
        Brendan Gregg <bgregg@...flix.com>,
        Joel Fernandes <joelaf@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        linux-rt-users@...r.kernel.org
Subject: Re: [RFC][PATCH 01/10] tracing: Do not reference event data in post
 call triggers

On Fri, 11 May 2018 15:49:28 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> From: "Steven Rostedt (VMware)" <rostedt@...dmis.org>
> 
> Trace event triggers can be called before or after the event has been
> committed. If it has been called after the commit, there's a possibility
> that the event no longer exists. Currently, the two post callers is the
> trigger to disable tracing (traceoff) and the one that will record a stack
> dump (stacktrace). Neither of them reference the trace event entry record,
> as that would lead to a race condition that could pass in corrupted data.
> 
> To prevent any other users of the post data triggers from using the trace
> event record, pass in NULL to the post call trigger functions for the event
> record, as they should never need to use them in the first place.
> 
> This does not fix any bug, but prevents bugs from happening by new post call
> trigger users.
> 

OK, so after commit the event record, the event handler should not access it.

Looks good to me.

Reviewed-by: Masami Hiramatsu <mhiramat@...nel.org>

Thanks,


> Signed-off-by: Steven Rostedt (VMware) <rostedt@...dmis.org>
> ---
>  include/linux/trace_events.h        | 3 +--
>  kernel/trace/trace.h                | 4 ++--
>  kernel/trace/trace_events_trigger.c | 6 ++----
>  3 files changed, 5 insertions(+), 8 deletions(-)
> 
> diff --git a/include/linux/trace_events.h b/include/linux/trace_events.h
> index 2bde3eff564c..d1c442d9bd85 100644
> --- a/include/linux/trace_events.h
> +++ b/include/linux/trace_events.h
> @@ -435,8 +435,7 @@ event_triggers_call(struct trace_event_file *file, void *rec,
>  		    struct ring_buffer_event *event);
>  extern void
>  event_triggers_post_call(struct trace_event_file *file,
> -			 enum event_trigger_type tt,
> -			 void *rec, struct ring_buffer_event *event);
> +			 enum event_trigger_type tt);
>  
>  bool trace_event_ignore_this_pid(struct trace_event_file *trace_file);
>  
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index 6fb46a06c9dc..24b666891eaf 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -1334,7 +1334,7 @@ event_trigger_unlock_commit(struct trace_event_file *file,
>  		trace_buffer_unlock_commit(file->tr, buffer, event, irq_flags, pc);
>  
>  	if (tt)
> -		event_triggers_post_call(file, tt, entry, event);
> +		event_triggers_post_call(file, tt);
>  }
>  
>  /**
> @@ -1367,7 +1367,7 @@ event_trigger_unlock_commit_regs(struct trace_event_file *file,
>  						irq_flags, pc, regs);
>  
>  	if (tt)
> -		event_triggers_post_call(file, tt, entry, event);
> +		event_triggers_post_call(file, tt);
>  }
>  
>  #define FILTER_PRED_INVALID	((unsigned short)-1)
> diff --git a/kernel/trace/trace_events_trigger.c b/kernel/trace/trace_events_trigger.c
> index d251cabcf69a..cc4148bfc01a 100644
> --- a/kernel/trace/trace_events_trigger.c
> +++ b/kernel/trace/trace_events_trigger.c
> @@ -97,7 +97,6 @@ EXPORT_SYMBOL_GPL(event_triggers_call);
>   * event_triggers_post_call - Call 'post_triggers' for a trace event
>   * @file: The trace_event_file associated with the event
>   * @tt: enum event_trigger_type containing a set bit for each trigger to invoke
> - * @rec: The trace entry for the event
>   *
>   * For each trigger associated with an event, invoke the trigger
>   * function registered with the associated trigger command, if the
> @@ -108,8 +107,7 @@ EXPORT_SYMBOL_GPL(event_triggers_call);
>   */
>  void
>  event_triggers_post_call(struct trace_event_file *file,
> -			 enum event_trigger_type tt,
> -			 void *rec, struct ring_buffer_event *event)
> +			 enum event_trigger_type tt)
>  {
>  	struct event_trigger_data *data;
>  
> @@ -117,7 +115,7 @@ event_triggers_post_call(struct trace_event_file *file,
>  		if (data->paused)
>  			continue;
>  		if (data->cmd_ops->trigger_type & tt)
> -			data->ops->func(data, rec, event);
> +			data->ops->func(data, NULL, NULL);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(event_triggers_post_call);
> -- 
> 2.17.0
> 
> 


-- 
Masami Hiramatsu <mhiramat@...nel.org>