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block: fix module reference leak on put_disk() call for cgroups throttle 

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
Signed-off-by: Jens Axboe <axboe@fb.com>
hifive-unleashed-5.1
Roman Pen 2016-02-09 12:33:35 -07:00 committed by Jens Axboe
parent 21d147880e
commit 39a169b62b
1 changed files with 9 additions and 0 deletions
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9
block/blk-cgroup.c
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@ -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);