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>
32eec68d2f