• Roman Pen's avatar
    block: fix module reference leak on put_disk() call for cgroups throttle · 39a169b6
    Roman Pen authored
    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;
    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)); \
        # lsmod | grep brd
        brd                     5175  100
    Now brd module has 100 references.
    The issue is fixed by calling module_put() just right away put_disk().
    Signed-off-by: default avatarRoman Pen <roman.penyaev@profitbricks.com>
    Cc: Gi-Oh Kim <gi-oh.kim@profitbricks.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Jens Axboe <axboe@kernel.dk>
    Cc: linux-block@vger.kernel.org
    Cc: linux-kernel@vger.kernel.org
    Signed-off-by: default avatarJens Axboe <axboe@fb.com>
blk-cgroup.c 35.8 KB