Messages in this thread | | | Subject | Re: [PATCH 1/4] block: fix module reference leak on put_disk() call for cgroups throttle | From | Gi-Oh Kim <> | Date | Wed, 3 Feb 2016 11:40:13 +0100 |
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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
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