On 12/15/2017 06:52 PM, Tejun Heo wrote:

Hello, Prateek.

On Fri, Dec 15, 2017 at 02:24:55PM +0530, Prateek Sood wrote:

quoted

Following are two ways to improve cgroup_transfer_tasks(). In
both cases task in PF_EXITING state would be left in source
cgroup. It would be removed from cgroup_exit() in exit path.

diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 024085d..e2bdcdb 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c

@@ -123,7 +123,10 @@ int cgroup_transfer_tasks(struct cgroup *to, struct cgroup *from)
         */
        do {
                css_task_iter_start(&from->self, 0, &it);
-               task = css_task_iter_next(&it);
+               do {
+                       task = css_task_iter_next(&it);
+               } while (task && (task & PF_EXITING))
+

Yeah, this looks good to me.  We can't just make a single pass as in
the other one because we can race aginst fork.  And PF_EXITING being
left behind is what was happening previously too anyway.  They can't
be moved.

Thanks.

Thanks TJ for reviewing.

I will send a formal patch with the above approved approach.


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