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

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Message-ID: <20150826135256.GI13340@dhcppc13.redhat.com>
Date:	Wed, 26 Aug 2015 19:22:56 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	Jeff Layton <jeff.layton@...marydata.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>,
	open list <linux-kernel@...r.kernel.org>,
	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 26/08/2015:09:13:02 AM, Jeff Layton wrote:
> 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.

Yes.

> 
> > +		__field(int, pid)
> > +		__field(unsigned long, flags)
> >  	),
> >  
> >  	TP_fast_assign(
> > -		__entry->xprt = xprt;
> > +		__entry->xprt = xprt,
> 
> Shouldn't that line end with ';'?
> 

I think, both should be OK.. I just copied this hunk from svc_xprt_dequeue.

> > +		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>

Thanks :-)

~Pratyush
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