Messages in this thread Patch in this message | | | From | Roman Pen <> | Subject | [PATCH 1/4] block: fix module reference leak on put_disk() call for cgroups throttle | Date | Mon, 1 Feb 2016 15:51:52 +0100 |
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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@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 --- block/blk-cgroup.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c index 5a37188..66e6f1a 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -788,6 +788,7 @@ int blkg_conf_prep(struct blkcg *blkcg, const struct blkcg_policy *pol, { 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, const struct blkcg_policy *pol, 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, const struct blkcg_policy *pol, 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); -- 2.6.2
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