4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Roman Pen <roman.penyaev@xxxxxxxxxxxxxxxx> commit 39a169b62b415390398291080dafe63aec751e0a upstream. 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. The issue is fixed by calling module_put() just right away put_disk(). Signed-off-by: Roman Pen <roman.penyaev@xxxxxxxxxxxxxxxx> Cc: Gi-Oh Kim <gi-oh.kim@xxxxxxxxxxxxxxxx> Cc: Tejun Heo <tj@xxxxxxxxxx> Cc: Jens Axboe <axboe@xxxxxxxxx> Cc: linux-block@xxxxxxxxxxxxxxx Cc: linux-kernel@xxxxxxxxxxxxxxx Signed-off-by: Jens Axboe <axboe@xxxxxx> Cc: Sumit Semwal <sumit.semwal@xxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- block/blk-cgroup.c | 9 +++++++++ 1 file changed, 9 insertions(+) --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -788,6 +788,7 @@ int blkg_conf_prep(struct blkcg *blkcg, { struct gendisk *disk; struct blkcg_gq *blkg; + struct module *owner; unsigned int major, minor; int key_len, part, ret; char *body; @@ -804,7 +805,9 @@ int blkg_conf_prep(struct blkcg *blkcg, if (!disk) return -ENODEV; if (part) { + owner = disk->fops->owner; put_disk(disk); + module_put(owner); return -ENODEV; } @@ -820,7 +823,9 @@ int blkg_conf_prep(struct blkcg *blkcg, ret = PTR_ERR(blkg); rcu_read_unlock(); spin_unlock_irq(disk->queue->queue_lock); + owner = disk->fops->owner; put_disk(disk); + module_put(owner); /* * If queue was bypassing, we should retry. Do so after a * short msleep(). It isn't strictly necessary but queue @@ -851,9 +856,13 @@ EXPORT_SYMBOL_GPL(blkg_conf_prep); void blkg_conf_finish(struct blkg_conf_ctx *ctx) __releases(ctx->disk->queue->queue_lock) __releases(rcu) { + struct module *owner; + spin_unlock_irq(ctx->disk->queue->queue_lock); rcu_read_unlock(); + owner = ctx->disk->fops->owner; put_disk(ctx->disk); + module_put(owner); } EXPORT_SYMBOL_GPL(blkg_conf_finish);