From mboxrd@z Thu Jan 1 00:00:00 1970 From: Li Zefan Subject: Re: [PATCH cgroup/for-3.11] cgroup: fix cgroupfs_root early destruction path Date: Wed, 26 Jun 2013 17:14:03 +0800 Message-ID: <51CAB0DB.5000706@huawei.com> References: <51C9D17B.5090208@oracle.com> <20130626010454.GD30407@mtj.dyndns.org> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130626010454.GD30407-9pTldWuhBndy/B6EtB590w@public.gmane.org> Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" To: Tejun Heo Cc: Sasha Levin , LKML , cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, trinity-u79uwXL29TY76Z2rM5mHXA@public.gmane.org On 2013/6/26 9:04, Tejun Heo wrote: > cgroupfs_root used to have ->actual_subsys_mask in addition to > ->subsys_mask. a8a648c4ac ("cgroup: remove > cgroup->actual_subsys_mask") removed it noting that the subsys_mask is > essentially temporary and doesn't belong in cgroupfs_root; however, > the patch made it impossible to tell whether a cgroupfs_root actually > has the subsystems bound or just have the bits set leading to the > following BUG when trying to mount with subsystems which are already > mounted elsewhere. > > kernel BUG at kernel/cgroup.c:1038! > invalid opcode: 0000 [#1] PREEMPT SMP DEBUG_PAGEALLOC > ... > CPU: 1 PID: 7973 Comm: mount Tainted: G W 3.10.0-rc7-next-20130625-sasha-00011-g1c1dc0e #1105 > task: ffff880fc0ae8000 ti: ffff880fc0b9a000 task.ti: ffff880fc0b9a000 > RIP: 0010:[] [] rebind_subsystems+0x409/0x5f0 > ... > Call Trace: > [] cgroup_kill_sb+0xff/0x210 > [] deactivate_locked_super+0x4f/0x90 > [] cgroup_mount+0x673/0x6e0 > [] cpuset_mount+0xd9/0x110 > [] mount_fs+0xb0/0x2d0 > [] vfs_kern_mount+0xbd/0x180 > [] do_new_mount+0x145/0x2c0 > [] do_mount+0x356/0x3c0 > [] SyS_mount+0xfd/0x140 > [] tracesys+0xdd/0xe2 > > We still want rebind_subsystems() to take added/removed masks, so > let's fix it by marking whether a cgroupfs_root has finished binding > or not. Also, document what's going on around ->subsys_mask > initialization so that similar mistakes aren't repeated. > > Signed-off-by: Tejun Heo > Reported-by: Sasha Levin Acked-by: Li Zefan