dm: table detect io beyond device
Patch
512875bd9661368da6f993205a61213b79ba1df0 in mainline.
This patch fixes a panic on shrinking a DM device if there is
outstanding I/O to the part of the device that is being removed.
(Normally this doesn't happen - a filesystem would be resized first,
for example.)
The bug is that __clone_and_map() assumes dm_table_find_target()
always returns a valid pointer. It may fail if a bio arrives from the
block layer but its target sector is no longer included in the DM
btree.
This patch appends an empty entry to table->targets[] which will
be returned by a lookup beyond the end of the device.
After calling dm_table_find_target(), __clone_and_map() and target_message()
check for this condition using
dm_target_is_valid().
Sample test script to trigger oops:
#!/bin/bash
FILE=$(mktemp)
LODEV=$(losetup -f)
MAP=$(basename ${FILE})
SIZE=4M
dd if=/dev/zero of=${FILE} bs=${SIZE} count=1
losetup ${LODEV} ${FILE}
echo "0 $(blockdev --getsz ${LODEV}) linear ${LODEV} 0" |dmsetup create ${MAP}
dmsetup suspend ${MAP}
echo "0 1 linear ${LODEV} 0" |dmsetup load ${MAP}
dd if=/dev/zero of=/dev/mapper/${MAP} bs=${SIZE} count=1 &
echo "Wait til dd push some I/O"
sleep 5
dmsetup resume ${MAP}
Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
Signed-off-by: Alasdair G Kergon <agk@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>