[SCSI] st: Take additional queue ref in st_probe

This patch fixes a reference count bug in the SCSI tape driver which can be
reproduced with the following:

* Boot with slub_debug=FZPU, tape drive attached
* echo 1 > /sys/devices/... tape device pci path .../remove
* Wait for device removal
* echo 1 > /sys/kernel/slab/blkdev_queue/validate
* Slub debug complains about corrupted poison pattern

In commit 523e1d39 (block: make gendisk hold a reference to its queue)
add_disk() and disk_release() were modified to get/put an additional
reference on a disk queue to fix a reference counting discrepency
between bdev release and SCSI device removal.  The ST driver never
calls add_disk(), so this commit introduced an extra kref put when the
ST driver frees its struct gendisk.

Attempts were made to fix this bug at the block level [1] but later
abandoned due to floppy driver issues [2].

[1] https://lkml.org/lkml/2012/8/27/354
[2] https://lkml.org/lkml/2012/9/22/113

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Tested-by: Ewan D. Milne <emilne@redhat.com>
Acked-by: Kai Mäkisara <Kai.Makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 86974471af68..2a32036a9404 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4112,6 +4112,10 @@ static int st_probe(struct device *dev)
         tpnt->disk = disk;
         disk->private_data = &tpnt->driver;
         disk->queue = SDp->request_queue;
+        /* SCSI tape doesn't register this gendisk via add_disk().  Manually
+         * take queue reference that release_disk() expects. */
+        if (!blk_get_queue(disk->queue))
+                goto out_put_disk;
         tpnt->driver = &st_template;
 
         tpnt->device = SDp;
@@ -4185,7 +4189,7 @@ static int st_probe(struct device *dev)
         idr_preload_end();
         if (error < 0) {
                 pr_warn("st: idr allocation failed: %d\n", error);
-                goto out_put_disk;
+                goto out_put_queue;
         }
         tpnt->index = error;
         sprintf(disk->disk_name, "st%d", tpnt->index);
@@ -4211,6 +4215,8 @@ out_remove_devs:
         spin_lock(&st_index_lock);
         idr_remove(&st_index_idr, tpnt->index);
         spin_unlock(&st_index_lock);
+out_put_queue:
+        blk_put_queue(disk->queue);
 out_put_disk:
         put_disk(disk);
         kfree(tpnt);