[PATCH v6 4/5] scsi: core: Add device reprobe support to scsi_rescan_device()

[Brian Bunker <brian@purestorage.com>]

Update INQUIRY data on rescan and call device_reprobe() if PQ or type
changed. Critical for ALUA unavailable state handling (SPC-4 5.15.2.4.4).

Co-developed-by: Krishna Kant <krishna.kant@purestorage.com>
Signed-off-by: Krishna Kant <krishna.kant@purestorage.com>
Reviewed-by: Hannes Reinecke <hare@kernel.org>
Signed-off-by: Brian Bunker <brian@purestorage.com>
---
 drivers/scsi/scsi_scan.c | 135 ++++++++++++++++++++++++++++++++++++---
 1 file changed, 125 insertions(+), 10 deletions(-)

diff --git a/drivers/scsi/scsi_scan.c b/drivers/scsi/scsi_scan.c
index 93a8719fcf26..ddb92282d49f 100644
--- a/drivers/scsi/scsi_scan.c
+++ b/drivers/scsi/scsi_scan.c
@@ -1097,6 +1097,83 @@ static unsigned char *scsi_inq_str(unsigned char *buf, unsigned char *inq,
 }
 #endif
 
+/**
+ * __scsi_reprobe_inquiry - Update INQUIRY data and reprobe device if needed
+ * @sdev: The SCSI device to reprobe
+ * @inq_result: Buffer containing fresh INQUIRY data
+ * @inq_len: Length of INQUIRY data
+ * @need_reprobe: Pointer to store whether device_reprobe() is needed
+ *
+ * Updates the device's INQUIRY data, attaches VPD pages, checks CDL support,
+ * and determines if the device needs to be reprobed due to any change in
+ * the standard INQUIRY data. If no reprobe is needed, calls driver rescan
+ * functions.
+ *
+ * This function does NOT take device_lock - caller must hold it.
+ *
+ * Returns:
+ *   SCSI_INQ_UNCHANGED on success (no reprobe needed)
+ *   SCSI_INQ_REPROBE_NEEDED if type or PQ changed (reprobe needed)
+ *  -ENOMEM on allocation failure
+ *  -EINVAL if INQUIRY data is too short
+ */
+static int __scsi_reprobe_inquiry(struct scsi_device *sdev,
+				  unsigned char *inq_result,
+				  size_t inq_len,
+				  bool *need_reprobe)
+{
+	struct device *dev = &sdev->sdev_gendev;
+	int ret;
+
+	/* Update INQUIRY data */
+	ret = scsi_update_inquiry_data(sdev, inq_result, inq_len);
+	if (ret < 0) {
+		sdev_printk(KERN_ERR, sdev,
+			    "failed to update inquiry data: %d\n", ret);
+		return ret;
+	}
+
+	SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
+		"updated inquiry data (type %d, PQ %d)\n",
+		sdev->type, sdev->inq_periph_qual));
+
+	/* Update VPD pages and CDL support */
+	scsi_attach_vpd(sdev);
+	scsi_cdl_check(sdev);
+
+	/*
+	 * If standard INQUIRY data changed, caller should reprobe to update
+	 * driver attachment. Any change in the first 36 bytes may affect
+	 * driver matching — PQ changes affect scsi_bus_match() which only
+	 * matches PQ == 0, and type changes require a different upper-layer
+	 * driver (e.g., sd for TYPE_DISK, sr for TYPE_ROM).
+	 */
+	if (ret == SCSI_INQ_REPROBE_NEEDED) {
+		SCSI_LOG_SCAN_BUS(3, sdev_printk(KERN_INFO, sdev,
+			"INQUIRY data changed, reprobe needed\n"));
+		*need_reprobe = true;
+		return ret;
+	}
+
+	/*
+	 * PQ and type unchanged, call driver's rescan functions to update
+	 * device properties (capacity, etc.)
+	 */
+	if (sdev->handler && sdev->handler->rescan)
+		sdev->handler->rescan(sdev);
+
+	if (dev->driver && try_module_get(dev->driver->owner)) {
+		struct scsi_driver *drv = to_scsi_driver(dev->driver);
+
+		if (drv->rescan)
+			drv->rescan(dev);
+		module_put(dev->driver->owner);
+	}
+
+	*need_reprobe = false;
+	return ret;
+}
+
 /**
  * scsi_probe_and_add_lun - probe a LUN, if a LUN is found add it
  * @shost:      SCSI host pointer
@@ -1661,7 +1738,11 @@ EXPORT_SYMBOL(scsi_resume_device);
 int scsi_rescan_device(struct scsi_device *sdev)
 {
 	struct device *dev = &sdev->sdev_gendev;
+	unsigned char *inq_result;
+	blist_flags_t bflags;
+	int result_len = 256;
 	int ret = 0;
+	bool need_reprobe = false;
 
 	device_lock(dev);
 
@@ -1677,18 +1758,52 @@ int scsi_rescan_device(struct scsi_device *sdev)
 		goto unlock;
 	}
 
-	scsi_attach_vpd(sdev);
-	scsi_cdl_check(sdev);
-
-	if (sdev->handler && sdev->handler->rescan)
-		sdev->handler->rescan(sdev);
+	/*
+	 * Rescan standard INQUIRY data to detect changes in device
+	 * properties (vendor, model, rev, peripheral qualifier, device type, etc.)
+	 */
+	inq_result = kmalloc(result_len, GFP_KERNEL);
+	if (inq_result) {
+		if (scsi_probe_lun(sdev, inq_result, result_len,
+				   &bflags) == 0) {
+			ret = __scsi_reprobe_inquiry(sdev, inq_result,
+						     max_t(size_t, sdev->inquiry_len, 36),
+						     &need_reprobe);
+			if (ret < 0) {
+				kfree(inq_result);
+				goto unlock;
+			}
+		}
+		kfree(inq_result);
+	}
 
-	if (dev->driver && try_module_get(dev->driver->owner)) {
-		struct scsi_driver *drv = to_scsi_driver(dev->driver);
+	/*
+	 * If INQUIRY data changed, reprobe to update driver attachment.
+	 * Must unlock device before calling device_reprobe() to avoid
+	 * deadlock. Hold a device reference across the unlock so sdev
+	 * cannot be freed while the lock is dropped. If another thread
+	 * changes INQUIRY data in this window, that thread's execution
+	 * will trigger the follow-on reprobe.
+	 */
+	if (need_reprobe) {
+		get_device(dev);
+		device_unlock(dev);
+		ret = device_reprobe(dev);
+		device_lock(dev);
+
+		if (sdev->sdev_state == SDEV_CANCEL ||
+		    sdev->sdev_state == SDEV_DEL) {
+			put_device(dev);
+			ret = -ENODEV;
+			goto unlock;
+		}
 
-		if (drv->rescan)
-			drv->rescan(dev);
-		module_put(dev->driver->owner);
+		if (ret < 0) {
+			sdev_printk(KERN_WARNING, sdev,
+				    "device reprobe failed, marking offline\n");
+			scsi_device_set_state(sdev, SDEV_OFFLINE);
+		}
+		put_device(dev);
 	}
 
 unlock:
-- 
2.55.0