[dm-devel] Re: [PATCH 07/23] io-controller: Common hierarchical fair queuing code in elevaotor layer

[Munehiro Ikeda <m-ikeda ds jp nec com>]

Hi,

Vivek Goyal wrote, on 08/28/2009 05:30 PM:
> +static struct io_group *io_find_alloc_group(struct request_queue *q,
> +			struct cgroup *cgroup, struct elv_fq_data *efqd,
> +			int create)
> +{
> +	struct io_cgroup *iocg = cgroup_to_io_cgroup(cgroup);
> +	struct io_group *iog = NULL;
> +	/* Note: Use efqd as key */
> +	void *key = efqd;
> +
> +	/*
> +	 * Take a refenrece to css object. Don't want to map a bio to
> +	 * a group if it has been marked for deletion
> +	 */
> +
> +	if (!css_tryget(&iocg->css))
> +		return iog;

cgroup_to_io_cgroup() returns NULL if only blkio subsystem
is mounted but io subsystem is not.  It can cause NULL pointer
access.

Signed-off-by: Munehiro "Muuhh" Ikeda <m-ikeda ds jp nec com>
---
 block/elevator-fq.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index b723c12..6714e73 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -1827,7 +1827,7 @@ static struct io_group *io_find_alloc_group(struct request_queue *q,
         * a group if it has been marked for deletion
         */
 
-       if (!css_tryget(&iocg->css))
+       if (!iocg || !css_tryget(&iocg->css))
                return iog;
 
        iog = io_cgroup_lookup_group(iocg, key);
-- 
1.6.2.5


-- 
IKEDA, Munehiro
  NEC Corporation of America
    m-ikeda ds jp nec com