linux-kernel - [PATCH AUTOSEL 4.9 25/29] scsi: zfcp: reduce flood of fcrscn1 trace records on multi-element RSCN

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Message-Id: <20190422194848.13049-25-sashal@kernel.org>
Date:   Mon, 22 Apr 2019 15:48:44 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Steffen Maier <maier@...ux.ibm.com>,
        "Martin K . Petersen" <martin.petersen@...cle.com>,
        Sasha Levin <sashal@...nel.org>, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.9 25/29] scsi: zfcp: reduce flood of fcrscn1 trace records on multi-element RSCN

From: Steffen Maier <maier@...ux.ibm.com>

[ Upstream commit c8206579175c34a2546de8a74262456278a7795a ]

If an incoming ELS of type RSCN contains more than one element, zfcp
suboptimally causes repeated erp trigger NOP trace records for each
previously failed port. These could be ports that went away.  It loops over
each RSCN element, and for each of those in an inner loop over all
zfcp_ports.

The trigger to recover failed ports should be just the reception of some
RSCN, no matter how many elements it has. So we can loop over failed ports
separately, and only then loop over each RSCN element to handle the
non-failed ports.

The call chain was:

  zfcp_fc_incoming_rscn
    for (i = 1; i < no_entries; i++)
      _zfcp_fc_incoming_rscn
        list_for_each_entry(port, &adapter->port_list, list)
          if (masked port->d_id match) zfcp_fc_test_link
          if (!port->d_id) zfcp_erp_port_reopen "fcrscn1"   <===

In order the reduce the "flooding" of the REC trace area in such cases, we
factor out handling the failed ports to be outside of the entries loop:

  zfcp_fc_incoming_rscn
    if (no_entries > 1)                                     <===
      list_for_each_entry(port, &adapter->port_list, list)  <===
        if (!port->d_id) zfcp_erp_port_reopen "fcrscn1"     <===
    for (i = 1; i < no_entries; i++)
      _zfcp_fc_incoming_rscn
        list_for_each_entry(port, &adapter->port_list, list)
          if (masked port->d_id match) zfcp_fc_test_link

Abbreviated example trace records before this code change:

Tag            : fcrscn1
WWPN           : 0x500507630310d327
ERP want       : 0x02
ERP need       : 0x02

Tag            : fcrscn1
WWPN           : 0x500507630310d327
ERP want       : 0x02
ERP need       : 0x00                 NOP => superfluous trace record

The last trace entry repeats if there are more than 2 RSCN elements.

Signed-off-by: Steffen Maier <maier@...ux.ibm.com>
Reviewed-by: Benjamin Block <bblock@...ux.ibm.com>
Reviewed-by: Jens Remus <jremus@...ux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@...cle.com>
Signed-off-by: Sasha Levin (Microsoft) <sashal@...nel.org>
---
 drivers/s390/scsi/zfcp_fc.c | 21 +++++++++++++++++----
 1 file changed, 17 insertions(+), 4 deletions(-)

diff --git a/drivers/s390/scsi/zfcp_fc.c b/drivers/s390/scsi/zfcp_fc.c
index 237688af179b..f7630cf581cd 100644
--- a/drivers/s390/scsi/zfcp_fc.c
+++ b/drivers/s390/scsi/zfcp_fc.c
@@ -238,10 +238,6 @@ static void _zfcp_fc_incoming_rscn(struct zfcp_fsf_req *fsf_req, u32 range,
 	list_for_each_entry(port, &adapter->port_list, list) {
 		if ((port->d_id & range) == (ntoh24(page->rscn_fid) & range))
 			zfcp_fc_test_link(port);
-		if (!port->d_id)
-			zfcp_erp_port_reopen(port,
-					     ZFCP_STATUS_COMMON_ERP_FAILED,
-					     "fcrscn1");
 	}
 	read_unlock_irqrestore(&adapter->port_list_lock, flags);
 }
@@ -249,6 +245,7 @@ static void _zfcp_fc_incoming_rscn(struct zfcp_fsf_req *fsf_req, u32 range,
 static void zfcp_fc_incoming_rscn(struct zfcp_fsf_req *fsf_req)
 {
 	struct fsf_status_read_buffer *status_buffer = (void *)fsf_req->data;
+	struct zfcp_adapter *adapter = fsf_req->adapter;
 	struct fc_els_rscn *head;
 	struct fc_els_rscn_page *page;
 	u16 i;
@@ -261,6 +258,22 @@ static void zfcp_fc_incoming_rscn(struct zfcp_fsf_req *fsf_req)
 	/* see FC-FS */
 	no_entries = head->rscn_plen / sizeof(struct fc_els_rscn_page);
 
+	if (no_entries > 1) {
+		/* handle failed ports */
+		unsigned long flags;
+		struct zfcp_port *port;
+
+		read_lock_irqsave(&adapter->port_list_lock, flags);
+		list_for_each_entry(port, &adapter->port_list, list) {
+			if (port->d_id)
+				continue;
+			zfcp_erp_port_reopen(port,
+					     ZFCP_STATUS_COMMON_ERP_FAILED,
+					     "fcrscn1");
+		}
+		read_unlock_irqrestore(&adapter->port_list_lock, flags);
+	}
+
 	for (i = 1; i < no_entries; i++) {
 		/* skip head and start with 1st element */
 		page++;
-- 
2.19.1