net/smc: Introduce tracepoint for smcr link down

SMC-R link down event is important to help us find links' issues, we
should track this event, especially in the single nic mode, which means
upper layer connection would be shut down. Then find out the direct
link-down reason in time, not only increased the counter, also the
location of the code who triggered this event.

Signed-off-by: Tony Lu <[e-mail]>
Reviewed-by: Wen Gu <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/smc/smc_core.c

···
 #include "smc_ism.h"
 #include "smc_netlink.h"
 #include "smc_stats.h"
+#include "smc_tracepoint.h"
 
 #define SMC_LGR_NUM_INCR		256
 #define SMC_LGR_FREE_DELAY_SERV		(600 * HZ)
···
 /* must be called under lgr->llc_conf_mutex lock */
 void smcr_link_down_cond(struct smc_link *lnk)
 {
-	if (smc_link_downing(&lnk->state))
+	if (smc_link_downing(&lnk->state)) {
+		trace_smcr_link_down(lnk, __builtin_return_address(0));
 		smcr_link_down(lnk);
+	}
 }
 
 /* will get the lgr->llc_conf_mutex lock */
 void smcr_link_down_cond_sched(struct smc_link *lnk)
 {
-	if (smc_link_downing(&lnk->state))
+	if (smc_link_downing(&lnk->state)) {
+		trace_smcr_link_down(lnk, __builtin_return_address(0));
 		schedule_work(&lnk->link_down_wrk);
+	}
 }
 
 void smcr_port_err(struct smc_ib_device *smcibdev, u8 ibport)

net/smc/smc_tracepoint.c

···
 EXPORT_TRACEPOINT_SYMBOL(smc_switch_to_fallback);
 EXPORT_TRACEPOINT_SYMBOL(smc_tx_sendmsg);
 EXPORT_TRACEPOINT_SYMBOL(smc_rx_recvmsg);
+EXPORT_TRACEPOINT_SYMBOL(smcr_link_down);

net/smc/smc_tracepoint.h

···
 	     TP_ARGS(smc, len)
 );
 
+TRACE_EVENT(smcr_link_down,
+
+	    TP_PROTO(const struct smc_link *lnk, void *location),
+
+	    TP_ARGS(lnk, location),
+
+	    TP_STRUCT__entry(
+			     __field(const void *, lnk)
+			     __field(const void *, lgr)
+			     __field(int, state)
+			     __string(name, lnk->ibname)
+			     __field(void *, location)
+	    ),
+
+	    TP_fast_assign(
+			   const struct smc_link_group *lgr = lnk->lgr;
+
+			   __entry->lnk = lnk;
+			   __entry->lgr = lgr;
+			   __entry->state = lnk->state;
+			   __assign_str(name, lnk->ibname);
+			   __entry->location = location;
+	    ),
+
+	    TP_printk("lnk=%p lgr=%p state=%d dev=%s location=%p",
+		      __entry->lnk, __entry->lgr,
+		      __entry->state, __get_str(name),
+		      __entry->location)
+);
+
 #endif /* _TRACE_SMC_H */
 
 #undef TRACE_INCLUDE_PATH