• Miao Xie's avatar
    cpuset: fix possible deadlock in async_rebuild_sched_domains · f90d4118
    Miao Xie authored
    Lockdep reported some possible circular locking info when we tested cpuset on
    NUMA/fake NUMA box.
    
    =======================================================
    [ INFO: possible circular locking dependency detected ]
    2.6.29-rc1-00224-ga6525042 #111
    -------------------------------------------------------
    bash/2968 is trying to acquire lock:
     (events){--..}, at: [<ffffffff8024c8cd>] flush_work+0x24/0xd8
    
    but task is already holding lock:
     (cgroup_mutex){--..}, at: [<ffffffff8026ad1e>] cgroup_lock_live_group+0x12/0x29
    
    which lock already depends on the new lock.
    ......
    -------------------------------------------------------
    
    Steps to reproduce:
    # mkdir /dev/cpuset
    # mount -t cpuset xxx /dev/cpuset
    # mkdir /dev/cpuset/0
    # echo 0 > /dev/cpuset/0/cpus
    # echo 0 > /dev/cpuset/0/mems
    # echo 1 > /dev/cpuset/0/memory_migrate
    # cat /dev/zero > /dev/null &
    # echo $! > /dev/cpuset/0/tasks
    
    This is because async_rebuild_sched_domains has the following lock sequence:
    run_workqueue(async_rebuild_sched_domains)
    	-> do_rebuild_sched_domains -> cgroup_lock
    
    But, attaching tasks when memory_migrate is set has following:
    cgroup_lock_live_group(cgroup_tasks_write)
    	-> do_migrate_pages -> flush_work
    
    This patch fixes it by using a separate workqueue thread.
    Signed-off-by: default avatarMiao Xie <miaox@cn.fujitsu.com>
    Signed-off-by: default avatarLai Jiangshan <laijs@cn.fujitsu.com>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    f90d4118
cpuset.c 73.5 KB