lkml.org 
[lkml]   [2009]   [Mar]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH -tip] cpuacct: Make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used.
    Balbir Singh wrote:
    > * Li Zefan <lizf@cn.fujitsu.com> [2009-03-17 14:28:11]:
    >
    >> Bharata B Rao wrote:
    >>> cpuacct: Make cpuacct hierarchy walk in cpuacct_charge() safe when
    >>> rcupreempt is used.
    >>>
    >>> cpuacct_charge() obtains task's ca and does a hierarchy walk upwards.
    >>> This can race with the task's movement between cgroups. This race
    >>> can cause an access to freed ca pointer in cpuacct_charge(). This will not
    >> Actually it can also end up access invalid tsk->cgroups. ;)
    >>
    >> get tsk->cgroups (cg)
    >> (move tsk to another cgroup) or (tsk exiting)
    >> -> kfree(tsk->cgroups)
    >> get cg->subsys[..]
    >>
    >
    > That problem should only occur if we dereference tsk->cgroups
    > separately and then use that to dereference cg->subsys. Since we use

    Do you mean tsk->cgroups->subsys is safe and
    cg = tsk->cgroups;...; cg->subsys is unsafe ?
    This is wrong.

    > task_subsys_state() and that is RCU safe, we should be OK.
    >

    Yes, it's RCU safe, which means it's unsafe without rcu_read_lock/unlock.


    \
     
     \ /
      Last update: 2009-03-18 02:43    [W:0.022 / U:29.560 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site