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:[<ffffffff81249b29>] [<ffffffff81249b29>] rebind_subsystems+0x409/0x5f0
> ...
> Call Trace:
> [<ffffffff8124bd4f>] cgroup_kill_sb+0xff/0x210
> [<ffffffff813d21af>] deactivate_locked_super+0x4f/0x90
> [<ffffffff8124f3b3>] cgroup_mount+0x673/0x6e0
> [<ffffffff81257169>] cpuset_mount+0xd9/0x110
> [<ffffffff813d2580>] mount_fs+0xb0/0x2d0
> [<ffffffff81404afd>] vfs_kern_mount+0xbd/0x180
> [<ffffffff814070b5>] do_new_mount+0x145/0x2c0
> [<ffffffff814085d6>] do_mount+0x356/0x3c0
> [<ffffffff8140873d>] SyS_mount+0xfd/0x140
> [<ffffffff854eb600>] 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 <tj@xxxxxxxxxx>
> Reported-by: Sasha Levin <sasha.levin@xxxxxxxxxx>
Acked-by: Li Zefan <lizefan@xxxxxxxxxx>
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