lkml.org 
[lkml]   [2016]   [Feb]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/4] block: fix module reference leak on put_disk() call for cgroups throttle
From
Date


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

\
 
 \ /
  Last update: 2016-02-03 12:01    [W:1.166 / U:0.028 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site