scsi: Rework handling of scsi_device.vpd_pg8[03]

Introduce struct scsi_vpd for the VPD page length, data and the RCU head
that will be used to free the VPD data. Use kfree_rcu() instead of
kfree() to free VPD data. Move the VPD buffer pointer check inside the
RCU read lock in the sysfs code. Only annotate pointers that are shared
across threads with __rcu. Use rcu_dereference() when dereferencing an
RCU pointer. This patch suppresses about twenty sparse complaints about
the vpd_pg8[03] pointers. This patch also fixes a race condition, namely
that updating of the VPD pointers and length variables in struct
scsi_device was not atomic with reference to the code reading these
variables. See also "Does the update code tolerate concurrent accesses?"
in Documentation/RCU/checklist.txt.

Fixes: commit 09e2b0b14690 ("scsi: rescan VPD attributes")
Signed-off-by: Bart Van Assche <bart.vanassche@wdc.com>
Acked-by: Hannes Reinecke <hare@suse.de>
Reviewed-by: Shane Seymour <shane.seymour@hpe.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Cc: Shane Seymour <shane.seymour@hpe.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

1 files changed, 20 insertions, 9 deletions

diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
index 5ed473a87589..bf53356f41f0 100644
--- a/drivers/scsi/scsi_sysfs.c
+++ b/drivers/scsi/scsi_sysfs.c
@@ -428,6 +428,7 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	struct scsi_device *sdev;
 	struct device *parent;
 	struct list_head *this, *tmp;
+	struct scsi_vpd *vpd_pg80 = NULL, *vpd_pg83 = NULL;
 	unsigned long flags;
 
 	sdev = container_of(work, struct scsi_device, ew.work);
@@ -456,8 +457,17 @@ static void scsi_device_dev_release_usercontext(struct work_struct *work)
 	/* NULL queue means the device can't be used */
 	sdev->request_queue = NULL;
 
-	kfree(sdev->vpd_pg83);
-	kfree(sdev->vpd_pg80);
+	mutex_lock(&sdev->inquiry_mutex);
+	rcu_swap_protected(sdev->vpd_pg80, vpd_pg80,
+			   lockdep_is_held(&sdev->inquiry_mutex));
+	rcu_swap_protected(sdev->vpd_pg83, vpd_pg83,
+			   lockdep_is_held(&sdev->inquiry_mutex));
+	mutex_unlock(&sdev->inquiry_mutex);
+
+	if (vpd_pg83)
+		kfree_rcu(vpd_pg83, rcu);
+	if (vpd_pg80)
+		kfree_rcu(vpd_pg80, rcu);
 	kfree(sdev->inquiry);
 	kfree(sdev);
 
@@ -795,15 +805,16 @@ show_vpd_##_page(struct file *filp, struct kobject *kobj,	\
 {									\
 	struct device *dev = container_of(kobj, struct device, kobj);	\
 	struct scsi_device *sdev = to_scsi_device(dev);			\
-	int ret;							\
-	if (!sdev->vpd_##_page)						\
-		return -EINVAL;						\
+	struct scsi_vpd *vpd_page;					\
+	int ret = -EINVAL;						\
+									\
 	rcu_read_lock();						\
-	ret = memory_read_from_buffer(buf, count, &off,			\
-				      rcu_dereference(sdev->vpd_##_page), \
-				       sdev->vpd_##_page##_len);	\
+	vpd_page = rcu_dereference(sdev->vpd_##_page);			\
+	if (vpd_page)							\
+		ret = memory_read_from_buffer(buf, count, &off,		\
+				vpd_page->data, vpd_page->len);		\
 	rcu_read_unlock();						\
-	return ret;						\
+	return ret;							\
 }									\
 static struct bin_attribute dev_attr_vpd_##_page = {		\
 	.attr =	{.name = __stringify(vpd_##_page), .mode = S_IRUGO },	\