rbd: don't drop the rbd_id too early

Currently an rbd device's id is released when it is removed, but it
is done before the code is run to clean up sysfs-related files (such
as /sys/bus/rbd/devices/1).

It's possible that an rbd is still in use after the rbd_remove()
call has been made.  It's essentially the same as an active inode
that stays around after it has been removed--until its final close
operation.  This means that the id shows up as free for reuse at a
time it should not be.

The effect of this was seen by Jens Rehpoehler, who:
    - had a filesystem mounted on an rbd device
    - unmapped that filesystem (without unmounting)
    - found that the mount still worked properly
    - but hit a panic when he attempted to re-map a new rbd device

This re-map attempt found the previously-unmapped id available.
The subsequent attempt to reuse it was met with a panic while
attempting to (re-)install the sysfs entry for the new mapped
device.

Fix this by holding off "putting" the rbd id, until the rbd_device
release function is called--when the last reference is finally
dropped.

Note: This fixes: http://tracker.newdream.net/issues/1907

Signed-off-by: Alex Elder <elder@dreamhost.com>
Signed-off-by: Sage Weil <sage@newdream.net>

diff --git a/drivers/block/rbd.c b/drivers/block/rbd.c
index 568fa5b..6bbd5af 100644 (file)
--- a/drivers/block/rbd.c
+++ b/drivers/block/rbd.c
@@ -2421,7 +2421,12 @@ static ssize_t rbd_add(struct bus_type *bus,
        if (rc)
                goto err_out_blkdev;
 
-       /* set up and announce blkdev mapping */
+       /*
+        * At this point cleanup in the event of an error is the job
+        * of the sysfs code (initiated by rbd_bus_del_dev()).
+        *
+        * Set up and announce blkdev mapping.
+        */
        rc = rbd_init_disk(rbd_dev);
        if (rc)
                goto err_out_bus;
@@ -2433,8 +2438,6 @@ static ssize_t rbd_add(struct bus_type *bus,
        return count;
 
 err_out_bus:
-       rbd_id_put(rbd_dev);
-
        /* this will also clean up rest of rbd_dev stuff */
 
        rbd_bus_del_dev(rbd_dev);
@@ -2492,6 +2495,9 @@ static void rbd_dev_release(struct device *dev)
        /* clean up and free blkdev */
        rbd_free_disk(rbd_dev);
        unregister_blkdev(rbd_dev->major, rbd_dev->name);
+
+       /* done with the id, and with the rbd_dev */
+       rbd_id_put(rbd_dev);
        kfree(rbd_dev);
 
        /* release module ref */
@@ -2524,8 +2530,6 @@ static ssize_t rbd_remove(struct bus_type *bus,
                goto done;
        }
 
-       rbd_id_put(rbd_dev);
-
        __rbd_remove_all_snaps(rbd_dev);
        rbd_bus_del_dev(rbd_dev);