On 01.02.2016 15:51, Roman Pen wrote:
get_disk(),get_gendisk() calls have non explicit side effect: they
increase the reference on the disk owner module.
The following is the correct sequence how to get a disk reference and
to put it:
disk = get_gendisk(...);
/* use disk */
owner = disk->fops->owner;
put_disk(disk);
module_put(owner);
fs/block_dev.c is aware of this required module_put() call, but f.e.
blkg_conf_finish(), which is located in block/blk-cgroup.c, does not put
a module reference. To see a leakage in action cgroups throttle config
can be used. In the following script I'm removing throttle for /dev/ram0
(actually this is NOP, because throttle was never set for this device):
# lsmod | grep brd
brd 5175 0
# i=100; while [ $i -gt 0 ]; do echo "1:0 0" > \
/sys/fs/cgroup/blkio/blkio.throttle.read_bps_device; i=$(($i - 1)); \
done
# lsmod | grep brd
brd 5175 100
Now brd module has 100 references.
I hope this patch would be merged into stable versions.
I've tested the patch with v3.12.45 on my server.
Before apply the patch, reference count was leaked.
# lsmod | grep loop
loop 16091 0
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 16091 1
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 16091 2
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 16091 3
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 16091 4
After apply the patch, reference count was still:
# lsmod | grep loop
loop 19171 0
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 19171 0
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 19171 0
# echo "7:0 1048576" > /sys/fs/cgroup/blkio/blkio.throttle.read_bps_device
# lsmod | grep loop
loop 19171 0
--
Best regards,
Gi-Oh Kim
