linux-kernel - [PATCH V3] net: sunrpc: fix tracepoint Warning: unknown op '->'

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Date:	Thu, 27 Aug 2015 10:01:33 +0530
From:	Pratyush Anand <panand@...hat.com>
To:	bfields@...ldses.org
Cc:	linux-nfs@...r.kernel.org, Pratyush Anand <panand@...hat.com>,
	Jeff Layton <jeff.layton@...marydata.com>,
	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),
	Trond Myklebust <trond.myklebust@...marydata.com>
Subject: [PATCH V3] net: sunrpc: fix tracepoint Warning: unknown op '->'

`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>
Reviewed-by: Jeff Layton <jeff.layton@...marydata.com>
Acked-by: Steven Rostedt <rostedt@...dmis.org>
---
Changes since V2:
- removed storing of "rqst" now
- removed replacement of , to ; at the end of statement __entry->xprt =
  xprt
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 | 21 ++++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index fd1a02cb3c82..003dca933803 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -529,18 +529,21 @@ TRACE_EVENT(svc_xprt_do_enqueue,
 
 	TP_STRUCT__entry(
 		__field(struct svc_xprt *, xprt)
-		__field(struct svc_rqst *, rqst)
+		__field_struct(struct sockaddr_storage, ss)
+		__field(int, pid)
+		__field(unsigned long, flags)
 	),
 
 	TP_fast_assign(
 		__entry->xprt = xprt;
-		__entry->rqst = rqst;
+		xprt ? memcpy(&__entry->ss, &xprt->xpt_remote, sizeof(__entry->ss)) : memset(&__entry->ss, 0, sizeof(__entry->ss));
+		__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 +592,20 @@ 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;
+		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 */
 
-- 
2.4.3

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