[PATCH v2 2/2] scsi: sas_user_scan: use scan_start if available

[Martin Wilck <martin.wilck@suse.com>]

Since 37c4e72b0651 ("scsi: Fix sas_user_scan() to handle wildcard and
multi-channel scans"), a wildcard scan on a SAS host scans all channels.
This can cause excessive resource usage and even system freeze with
some controllers, e.g. smartpqi. smartpqi and other drivers provide
the scan_start() and scan_finished() methods to scan devices
efficiently. Instead of blindly scanning every device, use these
methods to do the wildcard scan when available. Use the existing
function do_scsi_scan_host() for this purpose, which therefore needs
to be exported.

Fixes: 37c4e72b0651 ("scsi: Fix sas_user_scan() to handle wildcard and multi-channel scans")
Signed-off-by: Martin Wilck <mwilck@suse.com>
Cc: Don Brace <don.brace@microchip.com>
Cc: storagedev@microchip.com
Cc: Ranjan Kumar <ranjan.kumar@broadcom.com>
Cc: Sathya Prakash Veerichetty <sathya.prakash@broadcom.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumit Saxena <sumit.saxena@broadcom.com>
Cc: mpi3mr-linuxdrv.pdl@broadcom.com
Cc: MPT-FusionLinux.pdl@broadcom.com
Cc: Yihang Li <liyihang9@h-partners.com>
Cc: Jack Wang <jinpu.wang@cloud.ionos.com>
Cc: John Garry <john.g.garry@oracle.com>

----
This patch has been tested successfully with smartpqi, but it would
affect other drivers that provide scan_start(), and we don't have
hardware to test them all. Affected drivers are aic94xx, hisi_sas,
hpsa, isci, mpi3mr, mpt3sas, mvsas, pm8001, and smartpqi.
I cc'd the maintainers of these drivers above.
---
 drivers/scsi/scsi_scan.c          |  3 ++-
 drivers/scsi/scsi_transport_sas.c | 19 +++++++++++++++++++
 include/scsi/scsi_host.h          |  1 +
 3 files changed, 22 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 7b11bc7de0e3..05e0e50b6e42 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -2029,7 +2029,7 @@ static void scsi_finish_async_scan(struct async_scan_data *data)
 	kfree(data);
 }
 
-static void do_scsi_scan_host(struct Scsi_Host *shost)
+void do_scsi_scan_host(struct Scsi_Host *shost)
 {
 	if (shost->hostt->scan_finished) {
 		unsigned long start = jiffies;
@@ -2043,6 +2043,7 @@ static void do_scsi_scan_host(struct Scsi_Host *shost)
 				SCAN_WILD_CARD, SCSI_SCAN_INITIAL);
 	}
 }
+EXPORT_SYMBOL(do_scsi_scan_host);
 
 static void do_scan_async(void *_data, async_cookie_t c)
 {
diff --git a/drivers/scsi/scsi_transport_sas.c b/drivers/scsi/scsi_transport_sas.c
index 13412702188e..15600394dc31 100644
--- a/drivers/scsi/scsi_transport_sas.c
+++ b/drivers/scsi/scsi_transport_sas.c
@@ -1702,6 +1702,20 @@ static void scan_channel_zero(struct Scsi_Host *shost, uint id, u64 lun)
 	}
 }
 
+/*
+ * For wildcard scans on hosts that provide a scan_start method,
+ * use that instead of blindly scanning everything.
+ */
+static int sas_user_scan_with_scan_start(struct Scsi_Host *shost)
+{
+	if (!shost->hostt->scan_finished || !shost->hostt->scan_start)
+		return 1;
+
+	/* scan_finished exists, thus do_scsi_scan_host() will use it  */
+	do_scsi_scan_host(shost);
+	return 0;
+}
+
 /*
  * SCSI scan helper
  */
@@ -1721,6 +1735,11 @@ static int sas_user_scan(struct Scsi_Host *shost, uint channel,
 		break;
 
 	case SCAN_WILD_CARD:
+
+		if (id == SCAN_WILD_CARD && lun == SCAN_WILD_CARD
+			&& !sas_user_scan_with_scan_start(shost))
+			return 0;
+
 		mutex_lock(&sas_host->lock);
 		scan_channel_zero(shost, id, lun);
 		mutex_unlock(&sas_host->lock);
diff --git a/include/scsi/scsi_host.h b/include/scsi/scsi_host.h
index f6e12565a81d..9717559c5171 100644
--- a/include/scsi/scsi_host.h
+++ b/include/scsi/scsi_host.h
@@ -805,6 +805,7 @@ scsi_template_proc_dir(const struct scsi_host_template *sht);
 #else
 #define scsi_template_proc_dir(sht) NULL
 #endif
+extern void do_scsi_scan_host(struct Scsi_Host *shost);
 extern void scsi_scan_host(struct Scsi_Host *);
 extern int scsi_resume_device(struct scsi_device *sdev);
 extern int scsi_rescan_device(struct scsi_device *sdev);
-- 
2.53.0