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, 18 insertions, 26 deletions

diff --git a/drivers/scsi/scsi.c b/drivers/scsi/scsi.c
index f3f4926a3e77..d201ebcf4544 100644
--- a/drivers/scsi/scsi.c
+++ b/drivers/scsi/scsi.c
@@ -415,22 +415,20 @@ EXPORT_SYMBOL_GPL(scsi_get_vpd_page);
  * scsi_get_vpd_buf - Get Vital Product Data from a SCSI device
  * @sdev: The device to ask
  * @page: Which Vital Product Data to return
- * @len: Upon success, the VPD length will be stored in *@len.
  *
  * Returns %NULL upon failure.
  */
-static unsigned char *scsi_get_vpd_buf(struct scsi_device *sdev, u8 page,
-                                       int *len)
+static struct scsi_vpd *scsi_get_vpd_buf(struct scsi_device *sdev, u8 page)
 {
-        unsigned char *vpd_buf;
+        struct scsi_vpd *vpd_buf;
         int vpd_len = SCSI_VPD_PG_LEN, result;
 
 retry_pg:
-        vpd_buf = kmalloc(vpd_len, GFP_KERNEL);
+        vpd_buf = kmalloc(sizeof(*vpd_buf) + vpd_len, GFP_KERNEL);
         if (!vpd_buf)
                 return NULL;
 
-        result = scsi_vpd_inquiry(sdev, vpd_buf, page, vpd_len);
+        result = scsi_vpd_inquiry(sdev, vpd_buf->data, page, vpd_len);
         if (result < 0) {
                 kfree(vpd_buf);
                 return NULL;
@@ -441,31 +439,27 @@ retry_pg:
                 goto retry_pg;
         }
 
-        *len = result;
+        vpd_buf->len = result;
 
         return vpd_buf;
 }
 
 static void scsi_update_vpd_page(struct scsi_device *sdev, u8 page,
-                                 unsigned char __rcu **sdev_vpd_buf,
-                                 int *sdev_vpd_len)
+                                 struct scsi_vpd __rcu **sdev_vpd_buf)
 {
-        unsigned char *vpd_buf;
-        int len;
+        struct scsi_vpd *vpd_buf;
 
-        vpd_buf = scsi_get_vpd_buf(sdev, page, &len);
+        vpd_buf = scsi_get_vpd_buf(sdev, page);
         if (!vpd_buf)
                 return;
 
         mutex_lock(&sdev->inquiry_mutex);
         rcu_swap_protected(*sdev_vpd_buf, vpd_buf,
                            lockdep_is_held(&sdev->inquiry_mutex));
-        *sdev_vpd_len = len;
         mutex_unlock(&sdev->inquiry_mutex);
 
-        synchronize_rcu();
-
-        kfree(vpd_buf);
+        if (vpd_buf)
+                kfree_rcu(vpd_buf, rcu);
 }
 
 /**
@@ -479,24 +473,22 @@ static void scsi_update_vpd_page(struct scsi_device *sdev, u8 page,
  */
 void scsi_attach_vpd(struct scsi_device *sdev)
 {
-        int i, vpd_len;
-        unsigned char *vpd_buf;
+        int i;
+        struct scsi_vpd *vpd_buf;
 
         if (!scsi_device_supports_vpd(sdev))
                 return;
 
         /* Ask for all the pages supported by this device */
-        vpd_buf = scsi_get_vpd_buf(sdev, 0, &vpd_len);
+        vpd_buf = scsi_get_vpd_buf(sdev, 0);
         if (!vpd_buf)
                 return;
 
-        for (i = 4; i < vpd_len; i++) {
-                if (vpd_buf[i] == 0x80)
-                        scsi_update_vpd_page(sdev, 0x80, &sdev->vpd_pg80,
-                                             &sdev->vpd_pg80_len);
-                if (vpd_buf[i] == 0x83)
-                        scsi_update_vpd_page(sdev, 0x83, &sdev->vpd_pg83,
-                                             &sdev->vpd_pg83_len);
+        for (i = 4; i < vpd_buf->len; i++) {
+                if (vpd_buf->data[i] == 0x80)
+                        scsi_update_vpd_page(sdev, 0x80, &sdev->vpd_pg80);
+                if (vpd_buf->data[i] == 0x83)
+                        scsi_update_vpd_page(sdev, 0x83, &sdev->vpd_pg83);
         }
         kfree(vpd_buf);
 }