It seems that the root css doesn't have refcnt allocated(not needed?), and would cause the booting error attached. This patch tries to use css_get() to not increase the refcnt if parent is root. [ 0.792038] BUG: unable to handle kernel NULL pointer dereference at (null) [ 0.792937] IP: [<ffffffff810b37cc>] cgroup_mkdir+0x37c/0x740 [ 0.793027] PGD 0 [ 0.793027] Oops: 0002 [#1] [ 0.793027] Modules linked in: [ 0.793027] CPU: 0 PID: 1 Comm: systemd Not tainted 3.11.0-rc5-next-20130815+ #1 [ 0.793027] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007 [ 0.793027] task: ffff88007f868000 ti: ffff88007f864000 task.ti: ffff88007f864000 [ 0.793027] RIP: 0010:[<ffffffff810b37cc>] [<ffffffff810b37cc>] cgroup_mkdir+0x37c/0x740 [ 0.793027] RSP: 0018:ffff88007f865df8 EFLAGS: 00010246 [ 0.793027] RAX: 0000000000000000 RBX: ffffffff81a46ee0 RCX: 0000000000000001 [ 0.793027] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffffffff81a415c0 [ 0.793027] RBP: ffff88007f865ec8 R08: 0000000000000001 R09: 0000000000000000 [ 0.793027] R10: ffff88007ce6d060 R11: 0000000000000000 R12: ffff88007ce6d000 [ 0.793027] R13: ffff88007ce6d060 R14: ffffffff81a46d80 R15: ffff88007c6e8018 [ 0.793027] FS: 00007f13dbf6f840(0000) GS:ffffffff81a23000(0000) knlGS:0000000000000000 [ 0.793027] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 0.793027] CR2: 0000000000000000 CR3: 000000007b7e5000 CR4: 00000000000006b0 [ 0.793027] Stack: [ 0.793027] ffffffff810b380d 0000000000000002 ffff88007f865e18 ffffffff81167069 [ 0.793027] ffff88007f865ed8 ffffffff8116a3f5 ffff880037454400 ffff88007c6e8018 [ 0.793027] ffff88007c6e8028 ffff88007c6e8328 ffff88007c6e8000 ffff88007ce6d000 [ 0.793027] Call Trace: [ 0.793027] [<ffffffff810b380d>] ? cgroup_mkdir+0x3bd/0x740 [ 0.793027] [<ffffffff81167069>] ? lookup_hash+0x19/0x20 [ 0.793027] [<ffffffff8116a3f5>] ? kern_path_create+0x95/0x170 [ 0.793027] [<ffffffff8116ce3e>] vfs_mkdir+0x9e/0xf0 [ 0.793027] [<ffffffff8116d7a0>] SyS_mkdirat+0x60/0xe0 [ 0.793027] [<ffffffff8116d839>] SyS_mkdir+0x19/0x20 [ 0.793027] [<ffffffff814c960d>] tracesys+0xcf/0xd4 [ 0.793027] Code: ad 70 ff ff ff 48 89 9d 60 ff ff ff 4d 89 d5 4c 8b bd 68 ff ff ff 4c 8b 65 88 eb 50 0f 1f 00 48 8b 43 18 a8 03 0f 85 6c 03 00 00 <ff> 00 e8 1d 0a fb ff 85 c0 74 0d 80 3d f0 45 a1 00 00 0f 84 4c [ 0.793027] RIP [<ffffffff810b37cc>] cgroup_mkdir+0x37c/0x740 [ 0.793027] RSP <ffff88007f865df8> [ 0.793027] CR2: 0000000000000000 [ 0.827296] ---[ end trace a4b14b49bc46fd60 ]--- Signed-off-by: Li Zhong <zhong@xxxxxxxxxxxxxxxxxx> --- kernel/cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/cgroup.c b/kernel/cgroup.c index 723194f..781f8cd 100644 --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4485,7 +4485,7 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry, struct cgroup_subsys_state *css = css_ar[ss->subsys_id]; dget(dentry); - percpu_ref_get(&css->parent->refcnt); + css_get(css->parent); } /* hold a ref to the parent's dentry */ -- To unsubscribe from this list: send the line "unsubscribe linux-next" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
