[PATCH 2/6] scsi: Protect INQUIRY sysfs attributes with mutex

[Brian Bunker <brian@purestorage.com>]

The vendor, model, rev, and inquiry sysfs attributes read data directly
from the inquiry buffer. When INQUIRY data can be updated during device
rescan, these reads must be protected against concurrent updates.

Use the existing inquiry_mutex to protect access to these sysfs
attributes. This ensures that userspace always sees consistent INQUIRY
data, even if a rescan is updating the buffer concurrently.

This is preparatory work for adding INQUIRY data update support during
device rescan operations.

Signed-off-by: Brian Bunker <brian@purestorage.com>
Signed-off-by: Krishna Kant <krishna.kant@purestorage.com>
---
 drivers/scsi/scsi_sysfs.c | 74 +++++++++++++++++++++++++++++++++++----
 1 file changed, 67 insertions(+), 7 deletions(-)

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index dfc3559e7e04f..c34c69487205f 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -648,9 +648,63 @@ static DEVICE_ATTR(field, S_IRUGO, sdev_show_##field, NULL);
  */
 sdev_rd_attr (type, "%d\n");
 sdev_rd_attr (scsi_level, "%d\n");
-sdev_rd_attr (vendor, "%.8s\n");
-sdev_rd_attr (model, "%.16s\n");
-sdev_rd_attr (rev, "%.4s\n");
+
+/*
+ * Custom show functions for INQUIRY strings that take the inquiry_mutex.
+ * These strings point into the inquiry buffer which can be updated during
+ * device rescan, so we need to protect against concurrent access.
+ */
+static ssize_t
+sdev_show_vendor(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	ssize_t ret;
+
+	mutex_lock(&sdev->inquiry_mutex);
+	if (sdev->inquiry)
+		ret = snprintf(buf, 20, "%.*s\n", SCSI_INQ_VENDOR_LEN,
+			       scsi_inq_vendor(sdev->inquiry));
+	else
+		ret = snprintf(buf, 20, "\n");
+	mutex_unlock(&sdev->inquiry_mutex);
+	return ret;
+}
+static DEVICE_ATTR(vendor, S_IRUGO, sdev_show_vendor, NULL);
+
+static ssize_t
+sdev_show_model(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	ssize_t ret;
+
+	mutex_lock(&sdev->inquiry_mutex);
+	if (sdev->inquiry)
+		ret = snprintf(buf, 20, "%.*s\n", SCSI_INQ_PRODUCT_LEN,
+			       scsi_inq_product(sdev->inquiry));
+	else
+		ret = snprintf(buf, 20, "\n");
+	mutex_unlock(&sdev->inquiry_mutex);
+	return ret;
+}
+static DEVICE_ATTR(model, S_IRUGO, sdev_show_model, NULL);
+
+static ssize_t
+sdev_show_rev(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct scsi_device *sdev = to_scsi_device(dev);
+	ssize_t ret;
+
+	mutex_lock(&sdev->inquiry_mutex);
+	if (sdev->inquiry)
+		ret = snprintf(buf, 20, "%.*s\n", SCSI_INQ_REVISION_LEN,
+			       scsi_inq_revision(sdev->inquiry));
+	else
+		ret = snprintf(buf, 20, "\n");
+	mutex_unlock(&sdev->inquiry_mutex);
+	return ret;
+}
+static DEVICE_ATTR(rev, S_IRUGO, sdev_show_rev, NULL);
+
 sdev_rd_attr (cdl_supported, "%d\n");
 
 static ssize_t
@@ -915,12 +969,18 @@ static ssize_t show_inquiry(struct file *filep, struct kobject *kobj,
 {
 	struct device *dev = kobj_to_dev(kobj);
 	struct scsi_device *sdev = to_scsi_device(dev);
+	ssize_t ret;
 
-	if (!sdev->inquiry)
-		return -EINVAL;
+	mutex_lock(&sdev->inquiry_mutex);
+	if (!sdev->inquiry) {
+		ret = -EINVAL;
+	} else {
+		ret = memory_read_from_buffer(buf, count, &off, sdev->inquiry,
+					       sdev->inquiry_len);
+	}
+	mutex_unlock(&sdev->inquiry_mutex);
 
-	return memory_read_from_buffer(buf, count, &off, sdev->inquiry,
-				       sdev->inquiry_len);
+	return ret;
 }
 
 static const struct bin_attribute dev_attr_inquiry = {
-- 
2.50.1 (Apple Git-155)