linux-kernel - Re: [PATCH 2/2] net: sunrpc: fix trace print of &xprt->xpt

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Date:	Wed, 26 Aug 2015 16:30:18 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Jeff Layton <jlayton@...chiereds.net>
Cc:	Pratyush Anand <panand@...hat.com>, bfields@...ldses.org,
	linux-nfs@...r.kernel.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 2/2] net: sunrpc: fix trace print of &xprt->xpt_remote

On Wed, 26 Aug 2015 06:32:55 -0400
Jeff Layton <jlayton@...chiereds.net> wrote:

 
> >  	TP_fast_assign(
> > -		__entry->xprt = xprt,
> > -		xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));
> > +		__entry->xprt = xprt;
> > +		__entry->addr =
> > +			xprt ? (struct sockaddr *)&xprt->xpt_remote : NULL;
> 
> NAK, this is wrong. %pIScp will dereference that address so you don't

Ug, I hate that printk option. It can be dangerous.

> want to pass a NULL pointer to it. We do want to save a copy of the
> sockaddr.

Save just enough for what you need to print out. Don't waste any space
on the ring buffer that isn't necessary.

-- Steve

> 
> >  		__entry->flags = xprt ? xprt->xpt_flags : 0;
> >  	),
> >  
> >  	TP_printk("xprt=0x%p addr=%pIScp flags=%s", __entry->xprt,
> > -		(struct sockaddr *)&__entry->ss,
> > -		show_svc_xprt_flags(__entry->flags))
> > +		__entry->addr, show_svc_xprt_flags(__entry->flags))
> >  );
> >  
> >  TRACE_EVENT(svc_wake_up,
> 
> 

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