linux-kernel - Re: [PATCH V2] net: sunrpc: fix tracepoint Warning: unknown op '->'

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Date:	Wed, 26 Aug 2015 09:13:02 -0400
From:	Jeff Layton <jeff.layton@...marydata.com>
To:	Pratyush Anand <panand@...hat.com>
Cc:	bfields@...ldses.org, Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	"J. Bruce Fields" <bfields@...hat.com>,
	Jeff Layton <jlayton@...marydata.com>,
	linux-kernel@...r.kernel.org (open list),
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Trond Myklebust <trond.myklebust@...marydata.com>
Subject: Re: [PATCH V2] net: sunrpc: fix tracepoint Warning: unknown op '->'

On Wed, 26 Aug 2015 18:10:44 +0530
Pratyush Anand <panand@...hat.com> wrote:

> `perf stat  -e sunrpc:svc_xprt_do_enqueue true` results in
> 
> Warning: unknown op '->'
> Warning: [sunrpc:svc_xprt_do_enqueue] unknown op '->'
> 
> Similar warning for svc_handle_xprt as well.
> 
> Actually TP_printk() should never dereference an address saved in the ring
> buffer that points somewhere in the kernel. There's no guarantee that that
> object still exists (with the exception of static strings).
> 
> Therefore change all the arguments for TP_printk(), so that it references
> values existing in the ring buffer only.
> 
> While doing that, also fix another possible bug when argument xprt could be
> NULL and TP_fast_assign() tries to access it's elements.
> 
> Signed-off-by: Pratyush Anand <panand@...hat.com>
> Acked-by: Steven Rostedt <rostedt@...dmis.org>
> ---
> Changes since V1:
> - struct sockaddr memcopied to ring buffer so that its internal element can
> be accessed while printing %pIS.
> 
>  include/trace/events/sunrpc.h | 23 ++++++++++++++++-------
>  1 file changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
> index fd1a02cb3c82..75a16fcc0795 100644
> --- a/include/trace/events/sunrpc.h
> +++ b/include/trace/events/sunrpc.h
> @@ -529,18 +529,23 @@ TRACE_EVENT(svc_xprt_do_enqueue,
>  
>  	TP_STRUCT__entry(
>  		__field(struct svc_xprt *, xprt)
> +		__field_struct(struct sockaddr_storage, ss)
>  		__field(struct svc_rqst *, rqst)

nit: I think you should be able to avoid storing "rqst" now.

> +		__field(int, pid)
> +		__field(unsigned long, flags)
>  	),
>  
>  	TP_fast_assign(
> -		__entry->xprt = xprt;
> +		__entry->xprt = xprt,

Shouldn't that line end with ';'?

> +		xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));
>  		__entry->rqst = rqst;
> +		__entry->pid = rqst? rqst->rq_task->pid : 0;
> +		__entry->flags = xprt ? xprt->xpt_flags : 0;
>  	),
>  
>  	TP_printk("xprt=0x%p addr=%pIScp pid=%d flags=%s", __entry->xprt,
> -		(struct sockaddr *)&__entry->xprt->xpt_remote,
> -		__entry->rqst ? __entry->rqst->rq_task->pid : 0,
> -		show_svc_xprt_flags(__entry->xprt->xpt_flags))
> +		(struct sockaddr *)&__entry->ss,
> +		__entry->pid, show_svc_xprt_flags(__entry->flags))
>  );
>  
>  TRACE_EVENT(svc_xprt_dequeue,
> @@ -589,16 +594,20 @@ TRACE_EVENT(svc_handle_xprt,
>  	TP_STRUCT__entry(
>  		__field(struct svc_xprt *, xprt)
>  		__field(int, len)
> +		__field_struct(struct sockaddr_storage, ss)
> +		__field(unsigned long, flags)
>  	),
>  
>  	TP_fast_assign(
> -		__entry->xprt = xprt;
> +		__entry->xprt = xprt,
> +		xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));
>  		__entry->len = len;
> +		__entry->flags = xprt ? xprt->xpt_flags : 0;
>  	),
>  
>  	TP_printk("xprt=0x%p addr=%pIScp len=%d flags=%s", __entry->xprt,
> -		(struct sockaddr *)&__entry->xprt->xpt_remote, __entry->len,
> -		show_svc_xprt_flags(__entry->xprt->xpt_flags))
> +		(struct sockaddr *)&__entry->ss,
> +		__entry->len, show_svc_xprt_flags(__entry->flags))
>  );
>  #endif /* _TRACE_SUNRPC_H */
>  

Looks good otherwise. Thanks for fixing this!

Reviewed-by: Jeff Layton <jeff.layton@...marydata.com>
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