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/1907Signed-off-by: NAlex Elder <elder@dreamhost.com> Signed-off-by: NSage Weil <sage@newdream.net>
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