3.5.0-rc3 - Issue with CFQ and cgroup

[Paul Rolland <rol@as2917.net>]

Hello,

When I first booted my 3.5.0-rc3 config, I've some :
Default I/O scheduler not found. Using noop.
which surprised me. so, after the boot completed, I had a look at the
system messages, and found :

...
io scheduler noop registered
io scheduler deadline registered
------------[ cut here ]------------
WARNING: at block/blk-cgroup.c:867 blkcg_policy_register+0xb5/0xc0()
Hardware name: Vostro 1520
Modules linked in:
Pid: 1, comm: swapper/0 Not tainted 3.5.0-rc3 #1
Call Trace:
 [<ffffffff8103a59a>] warn_slowpath_common+0x7a/0xb0
 [<ffffffff81cafbed>] ? deadline_init+0x12/0x12
 [<ffffffff8103a5e5>] warn_slowpath_null+0x15/0x20
 [<ffffffff8131a6f5>] blkcg_policy_register+0xb5/0xc0
 [<ffffffff81cafc2f>] cfq_init+0x42/0x9f
 [<ffffffff810001ba>] do_one_initcall+0x3a/0x160
 [<ffffffff81c8ed08>] kernel_init+0x137/0x1bb
 [<ffffffff81c8e5c5>] ? do_early_param+0x87/0x87
 [<ffffffff8169e3d4>] kernel_thread_helper+0x4/0x10
 [<ffffffff81c8ebd1>] ? start_kernel+0x3b2/0x3b2
 [<ffffffff8169e3d0>] ? gs_change+0xb/0xb
---[ end trace 82bc55f036371117 ]---

So, at the time cfq should have registered, something went wrong.
It looks that this comes from my config defining CFQ, CGROUP but no
CFQ_CGROUP_IOSCHED.
...
CONFIG_CGROUPS=y
CONFIG_IOSCHED_CFQ=y
# CONFIG_CFQ_GROUP_IOSCHED is not set
...

as the code is :
static struct blkcg_policy blkcg_policy_cfq __maybe_unused;
...
#ifdef CONFIG_CFQ_GROUP_IOSCHED
static struct blkcg_policy blkcg_policy_cfq = {
        .pd_size                = sizeof(struct cfq_group),
        .cftypes                = cfq_blkcg_files,
        
        .pd_init_fn             = cfq_pd_init,
        .pd_reset_stats_fn      = cfq_pd_reset_stats,
};
#endif
...
static int __init cfq_init(void)
{
...
        ret = blkcg_policy_register(&blkcg_policy_cfq);


Not sure what's the best fix is... Could someone shed some light on this ?

Paul

PS: Just checked 3.5-rc4, source code there is the same.