From: David Milburn <dmilburn@redhat.com>
Date: Wed, 12 Aug 2009 13:26:45 -0500
Subject: [scsi] scsi_transport_fc: fc_user_scan correction
Message-id: 20090812182645.GA6115@dhcp-210.hsv.redhat.com
O-Subject: [RHEL5.5 PATCH] scsi_transport_fc: fc_user_scan correction
Bugzilla: 515176
RH-Acked-by: Mike Christie <mchristi@redhat.com>
RH-Acked-by: Dean Nelson <dnelson@redhat.com>

In RHEL5, locking around the FC remote port list
is needed when user initiates a re-scan of the
host.

# echo "- - -" > /sys/class/scsi_host/hostN/scan

Otherwise, fc_user_scan may hang processing the
list resulting in a soft lockup.

BUG: soft lockup detected on CPU#1!
 [<c044d21c>] softlockup_tick+0x96/0xa4
 [<c042ddb0>] update_process_times+0x39/0x5c
 [<c04196fb>] smp_apic_timer_interrupt+0x5b/0x6c
 [<c04059bf>] apic_timer_interrupt+0x1f/0x24
 [<f88aeccd>] fc_user_scan+0x69/0x72 [scsi_transport_fc]
 [<f88aec64>] fc_user_scan+0x0/0x72 [scsi_transport_fc]
 [<f88704bb>] store_scan+0x83/0xab [scsi_mod]
 [<f8870438>] store_scan+0x0/0xab [scsi_mod]
 [<c054cd24>] class_device_attr_store+0x1b/0x1f
 [<c04a4a3c>] sysfs_write_file+0x91/0xbb
 [<c04a49ab>] sysfs_write_file+0x0/0xbb
 [<c0470254>] vfs_write+0xa1/0x143
 [<c0470846>] sys_write+0x3c/0x63
 [<c0404eff>] syscall_call+0x7/0xb

Upstream commit:

commit bda232531f0c117921690ee3c060953c8f12e5a1
Author: James Smart <James.Smart@Emulex.Com>
Date:   Thu Apr 24 12:12:46 2008 -0400

    [SCSI] scsi_transport_fc: fc_user_scan correction

    Way back when, when the fc_user_scan routine was created, it kept some
    of its original logic that walked the rport list and kicked off a scan.
    Unfortunately, it didn't keep any of the locking around the rport list,
    nor did it consider the synchronous nature of the scan invoked. The result,
    there are some scan requests where the rport list changes, thus a subsequen\t
    scan is called on a bogus rport structure and the system NMI's.

This resolves BZ 515176, Fujitsu has verified a
-162.el5 kernel built with this patch. Please
review and ACK.

Thanks,
David

 drivers/scsi/scsi_transport_fc.c |   60 +++++++++++++++++++++++++++++++++----
 1 files changed, 53 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/scsi_transport_fc.c b/drivers/scsi/scsi_transport_fc.c
index 3b18179..0534988 100644
--- a/drivers/scsi/scsi_transport_fc.c
+++ b/drivers/scsi/scsi_transport_fc.c
@@ -1450,12 +1450,17 @@ fc_timed_out(struct scsi_cmnd *scmd)
 }
 
 /*
- * Must be called with shost->host_lock held
+ * Called by fc_user_scan to locate an rport on the shost that
+ * matches the channel and target id, and invoke scsi_scan_target()
+ * on the rport.
  */
-static int fc_user_scan(struct Scsi_Host *shost, uint channel,
-		uint id, uint lun)
+static void
+fc_user_scan_tgt(struct Scsi_Host *shost, uint channel, uint id, uint lun)
 {
 	struct fc_rport *rport;
+	unsigned long flags;
+
+	spin_lock_irqsave(shost->host_lock, flags);
 
 	list_for_each_entry(rport, &fc_host_rports(shost), peers) {
 		if (rport->scsi_target_id == -1)
@@ -1464,13 +1469,54 @@ static int fc_user_scan(struct Scsi_Host *shost, uint channel,
 		if (rport->port_state != FC_PORTSTATE_ONLINE)
 			continue;
 
-		if ((channel == SCAN_WILD_CARD || channel == rport->channel) &&
-		    (id == SCAN_WILD_CARD || id == rport->scsi_target_id)) {
-			scsi_scan_target(&rport->dev, rport->channel,
-					 rport->scsi_target_id, lun, 1);
+		if ((channel == rport->channel) &&
+		    (id == rport->scsi_target_id)) {
+			spin_unlock_irqrestore(shost->host_lock, flags);
+			scsi_scan_target(&rport->dev, channel, id, lun, 1);
+			return;
 		}
 	}
 
+	spin_unlock_irqrestore(shost->host_lock, flags);
+}
+
+/*
+ * Called via sysfs scan routines. Necessary, as the FC transport
+ * wants to place all target objects below the rport object. So this
+ * routine must invoke the scsi_scan_target() routine with the rport
+ * object as the parent.
+ */
+static int
+fc_user_scan(struct Scsi_Host *shost, uint channel, uint id, uint lun)
+{
+	uint chlo, chhi;
+	uint tgtlo, tgthi;
+
+	if (((channel != SCAN_WILD_CARD) && (channel > shost->max_channel)) ||
+	    ((id != SCAN_WILD_CARD) && (id >= shost->max_id)) ||
+	    ((lun != SCAN_WILD_CARD) && (lun > shost->max_lun)))
+		return -EINVAL;
+
+	if (channel == SCAN_WILD_CARD) {
+		chlo = 0;
+		chhi = shost->max_channel + 1;
+	} else {
+		chlo = channel;
+		chhi = channel + 1;
+	}
+
+	if (id == SCAN_WILD_CARD) {
+		tgtlo = 0;
+		tgthi = shost->max_id;
+	} else {
+		tgtlo = id;
+		tgthi = id + 1;
+	}
+
+	for ( ; chlo < chhi; chlo++)
+		for ( ; tgtlo < tgthi; tgtlo++)
+			fc_user_scan_tgt(shost, chlo, tgtlo, lun);
+
 	return 0;
 }