[PATCH 3.16 323/410] bcache: don't attach backing with duplicate UUID

[Ben Hutchings]

3.16.57-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Michael Lyle <mlyle@xxxxxxxx>

commit 86755b7a96faed57f910f9e6b8061e019ac1ec08 upstream.

This can happen e.g. during disk cloning.

This is an incomplete fix: it does not catch duplicate UUIDs earlier
when things are still unattached.  It does not unregister the device.
Further changes to cope better with this are planned but conflict with
Coly's ongoing improvements to handling device errors.  In the meantime,
one can manually stop the device after this has happened.

Attempts to attach a duplicate device result in:

[  136.372404] loop: module loaded
[  136.424461] bcache: register_bdev() registered backing device loop0
[  136.424464] bcache: bch_cached_dev_attach() Tried to attach loop0 but duplicate UUID already attached

My test procedure is:

  dd if=/dev/sdb1 of=imgfile bs=1024 count=262144
  losetup -f imgfile

Signed-off-by: Michael Lyle <mlyle@xxxxxxxx>
Reviewed-by: Tang Junhui <tang.junhui@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 drivers/md/bcache/super.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -964,6 +964,7 @@ int bch_cached_dev_attach(struct cached_
 	uint32_t rtime = cpu_to_le32(get_seconds());
 	struct uuid_entry *u;
 	char buf[BDEVNAME_SIZE];
+	struct cached_dev *exist_dc, *t;
 
 	bdevname(dc->bdev, buf);
 
@@ -987,6 +988,16 @@ int bch_cached_dev_attach(struct cached_
 		return -EINVAL;
 	}
 
+	/* Check whether already attached */
+	list_for_each_entry_safe(exist_dc, t, &c->cached_devs, list) {
+		if (!memcmp(dc->sb.uuid, exist_dc->sb.uuid, 16)) {
+			pr_err("Tried to attach %s but duplicate UUID already attached",
+				buf);
+
+			return -EINVAL;
+		}
+	}
+
 	u = uuid_find(c, dc->sb.uuid);
 
 	if (u &&