net/smc: Introduce tracepoint for fallback

This introduces tracepoint for smc fallback to TCP, so that we can track
which connection and why it fallbacks, and map the clcsocks' pointer with
/proc/net/tcp to find more details about TCP connections. Compared with
kprobe or other dynamic tracing, tracepoints are stable and easy to use.

Signed-off-by: Tony Lu <tonylu@linux.alibaba.com>
Reviewed-by: Wen Gu <guwen@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/smc/Makefile

@@ -1,5 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0-only
+ccflags-y += -I$(src)
 obj-$(CONFIG_SMC)	+= smc.o
 obj-$(CONFIG_SMC_DIAG)	+= smc_diag.o
 smc-y := af_smc.o smc_pnet.o smc_ib.o smc_clc.o smc_core.o smc_wr.o smc_llc.o
 smc-y += smc_cdc.o smc_tx.o smc_rx.o smc_close.o smc_ism.o smc_netlink.o smc_stats.o
+smc-y += smc_tracepoint.o

net/smc/af_smc.c

@@ -50,6 +50,7 @@
 #include "smc_rx.h"
 #include "smc_close.h"
 #include "smc_stats.h"
+#include "smc_tracepoint.h"
 
 static DEFINE_MUTEX(smc_server_lgr_pending);	/* serialize link group
 						 * creation on server
@@ -564,6 +565,7 @@ static void smc_switch_to_fallback(struct smc_sock *smc, int reason_code)
 	smc->use_fallback = true;
 	smc->fallback_rsn = reason_code;
 	smc_stat_fallback(smc);
+	trace_smc_switch_to_fallback(smc, reason_code);
 	if (smc->sk.sk_socket && smc->sk.sk_socket->file) {
 		smc->clcsock->file = smc->sk.sk_socket->file;
 		smc->clcsock->file->private_data = smc->clcsock;

net/smc/smc_tracepoint.c

@@ -0,0 +1,6 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+#define CREATE_TRACE_POINTS
+#include "smc_tracepoint.h"
+
+EXPORT_TRACEPOINT_SYMBOL(smc_switch_to_fallback);

net/smc/smc_tracepoint.h

@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM smc
+
+#if !defined(_TRACE_SMC_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_SMC_H
+
+#include <linux/ipv6.h>
+#include <linux/tcp.h>
+#include <linux/tracepoint.h>
+#include <net/ipv6.h>
+#include "smc.h"
+#include "smc_core.h"
+
+TRACE_EVENT(smc_switch_to_fallback,
+
+	    TP_PROTO(const struct smc_sock *smc, int fallback_rsn),
+
+	    TP_ARGS(smc, fallback_rsn),
+
+	    TP_STRUCT__entry(
+			     __field(const void *, sk)
+			     __field(const void *, clcsk)
+			     __field(int, fallback_rsn)
+	    ),
+
+	    TP_fast_assign(
+			   const struct sock *sk = &smc->sk;
+			   const struct sock *clcsk = smc->clcsock->sk;
+
+			   __entry->sk = sk;
+			   __entry->clcsk = clcsk;
+			   __entry->fallback_rsn = fallback_rsn;
+	    ),
+
+	    TP_printk("sk=%p clcsk=%p fallback_rsn=%d",
+		      __entry->sk, __entry->clcsk, __entry->fallback_rsn)
+);
+
+#endif /* _TRACE_SMC_H */
+
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE smc_tracepoint
+
+#include <trace/define_trace.h>