[SCSI] st: Take additional queue ref in st_probe

Joe Lawrence · James Bottomley · commit 2b5bebccd282 · 2013-04-06T11:14:20.000+01:00
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 523e1d3 (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>
diff --git 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 @@ static int st_probe(struct device *dev)
 	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);
