于 2014/9/2 23:33, Tejun Heo 写道:
> Hello, Li.
>
> On Tue, Sep 02, 2014 at 06:56:58PM +0800, Li Zefan wrote:
>> for ((; ;))
>> {
>> echo $$ > /cgroup/sub/cgroup.procs
>> ech $$ > /cgce 6f2e0c38c2108a74 ]---
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> copy & paste error?
> ...
oops
>> Reported-by: Toralf Förster <toralf.foerster@xxxxxx>
>> Signed-off-by: Li Zefan <lizefan@xxxxxxxxxx>
>> ---
>>
>> Toralf, Thanks for reporting the bug. I'm not able to repy to your email,
>> because I was kicked out of the cgroup mailing list so didn't receive
>> emails from mailing list for a week.
>>
>> ---
>> kernel/cgroup.c | 19 +++++++++----------
>> 1 file changed, 9 insertions(+), 10 deletions(-)
>>
>> diff --git a/kernel/cgroup.c b/kernel/cgroup.c
>> index 1c56924..e03fc62 100644
>> --- a/kernel/cgroup.c
>> +++ b/kernel/cgroup.c
>> @@ -4185,6 +4185,15 @@ static void css_release_work_fn(struct work_struct *work)
>>
>> mutex_unlock(&cgroup_mutex);
>>
>> + /*
>> + * There are two control paths which try to determine cgroup from
>> + * dentry without going through kernfs - cgroupstats_build() and
>> + * css_tryget_online_from_dir(). Those are supported by RCU
>> + * protecting clearing of cgrp->kn->priv backpointer.
>> + */
>> + if (!ss && cgroup_parent(cgrp))
>> + RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
>
> Can we move the above into the preceding else block? I don't think
> holding cgroup_mutex or not makes any difference here.
> Also, why do
> we need the cgroup_parent() check? Do we deref root's kn->priv in the
> destruction path? If so, can you please note that in the comment?
>
I think the check is not necessary. I was trying to make smaller difference
than the original code, and RCU_INIT_POINTER() is in cgroup_rmdir() which
won't be called on root cgroup.
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