[PATCH v1] SUNRPC: Fix a NULL pointer deref in trace_svc_stats_latency()

[Chuck Lever <chuck.lever@xxxxxxxxxx>]

Some paths through svc_process() leave rqst->rq_procinfo set to
NULL, which triggers a crash if tracing happens to be enabled.

Fixes: 89ff87494c6e ("SUNRPC: Display RPC procedure names instead of proc numbers")
Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
---
 include/linux/sunrpc/svc.h    |    1 +
 include/trace/events/sunrpc.h |    8 ++++----
 net/sunrpc/svc.c              |   15 +++++++++++++++
 3 files changed, 20 insertions(+), 4 deletions(-)

diff --git a/include/linux/sunrpc/svc.h b/include/linux/sunrpc/svc.h
index dd3daadbc0e5..064c96157d1f 100644
--- a/include/linux/sunrpc/svc.h
+++ b/include/linux/sunrpc/svc.h
@@ -527,6 +527,7 @@ void		   svc_wake_up(struct svc_serv *);
 void		   svc_reserve(struct svc_rqst *rqstp, int space);
 struct svc_pool *  svc_pool_for_cpu(struct svc_serv *serv, int cpu);
 char *		   svc_print_addr(struct svc_rqst *, char *, size_t);
+const char *	   svc_proc_name(const struct svc_rqst *rqstp);
 int		   svc_encode_result_payload(struct svc_rqst *rqstp,
 					     unsigned int offset,
 					     unsigned int length);
diff --git a/include/trace/events/sunrpc.h b/include/trace/events/sunrpc.h
index 174385da20ad..b10de4896147 100644
--- a/include/trace/events/sunrpc.h
+++ b/include/trace/events/sunrpc.h
@@ -1641,7 +1641,7 @@ TRACE_EVENT(svc_process,
 		__field(u32, vers)
 		__field(u32, proc)
 		__string(service, name)
-		__string(procedure, rqst->rq_procinfo->pc_name)
+		__string(procedure, svc_proc_name(rqst))
 		__string(addr, rqst->rq_xprt ?
 			 rqst->rq_xprt->xpt_remotebuf : "(null)")
 	),
@@ -1651,7 +1651,7 @@ TRACE_EVENT(svc_process,
 		__entry->vers = rqst->rq_vers;
 		__entry->proc = rqst->rq_proc;
 		__assign_str(service, name);
-		__assign_str(procedure, rqst->rq_procinfo->pc_name);
+		__assign_str(procedure, svc_proc_name(rqst));
 		__assign_str(addr, rqst->rq_xprt ?
 			     rqst->rq_xprt->xpt_remotebuf : "(null)");
 	),
@@ -1917,7 +1917,7 @@ TRACE_EVENT(svc_stats_latency,
 	TP_STRUCT__entry(
 		__field(u32, xid)
 		__field(unsigned long, execute)
-		__string(procedure, rqst->rq_procinfo->pc_name)
+		__string(procedure, svc_proc_name(rqst))
 		__string(addr, rqst->rq_xprt->xpt_remotebuf)
 	),
 
@@ -1925,7 +1925,7 @@ TRACE_EVENT(svc_stats_latency,
 		__entry->xid = be32_to_cpu(rqst->rq_xid);
 		__entry->execute = ktime_to_us(ktime_sub(ktime_get(),
 							 rqst->rq_stime));
-		__assign_str(procedure, rqst->rq_procinfo->pc_name);
+		__assign_str(procedure, svc_proc_name(rqst));
 		__assign_str(addr, rqst->rq_xprt->xpt_remotebuf);
 	),
 
diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 1f3552c62e71..35b549c147a2 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1633,6 +1633,21 @@ u32 svc_max_payload(const struct svc_rqst *rqstp)
 }
 EXPORT_SYMBOL_GPL(svc_max_payload);
 
+/**
+ * svc_proc_name - Return RPC procedure name in string form
+ * @rqstp: svc_rqst to operate on
+ *
+ * Return value:
+ *   Pointer to a NUL-terminated string
+ */
+const char *svc_proc_name(const struct svc_rqst *rqstp)
+{
+	if (rqstp && rqstp->rq_procinfo)
+		return rqstp->rq_procinfo->pc_name;
+	return "unknown";
+}
+
+
 /**
  * svc_encode_result_payload - mark a range of bytes as a result payload
  * @rqstp: svc_rqst to operate on