On Wed, 2017-07-05 at 11:28 -0400, Tejun Heo wrote:
> Hello, Abdul.
>
> Thanks for the debug info. Can you please see whether the following
> patch fixes the issue?
It is my pleasure and yes the patch fixes the problem.
> If the problem is too difficult to reproduce
The problem was reproducible all the time.
With the patch fix, I tried multiple times and long runs of cpu off-on
cycles but no Oops is seen.
Thank you for spending your valuable time on fixing this issue.
Reported-and-tested-by : Abdul Haleem <abdha...@linux.vnet.ibm.com>
> to confirm the fix by seeing whether it no longer triggers, please let
> me know. We can instead apply a patch which triggers WARN on the
> failing condition to confirm the diagnosis.
>
> Thanks.
>
> diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
> index 793565c05742..8b4c3c2f2509 100644
> --- a/kernel/cgroup/cgroup-internal.h
> +++ b/kernel/cgroup/cgroup-internal.h
> @@ -33,6 +33,9 @@ struct cgroup_taskset {
> struct list_head src_csets;
> struct list_head dst_csets;
>
> + /* the number of tasks in the set */
> + int nr_tasks;
> +
> /* the subsys currently being processed */
> int ssid;
>
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index dbfd7028b1c6..e3c4152741a3 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -1954,6 +1954,8 @@ static void cgroup_migrate_add_task(struct task_struct
> *task,
> if (!cset->mg_src_cgrp)
> return;
>
> + mgctx->tset.nr_tasks++;
> +
> list_move_tail(&task->cg_list, &cset->mg_tasks);
> if (list_empty(&cset->mg_node))
> list_add_tail(&cset->mg_node,
> @@ -2047,16 +2049,18 @@ static int cgroup_migrate_execute(struct cgroup_mgctx
> *mgctx)
> return 0;
>
> /* check that we can legitimately attach to the cgroup */
> - do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> - if (ss->can_attach) {
> - tset->ssid = ssid;
> - ret = ss->can_attach(tset);
> - if (ret) {
> - failed_ssid = ssid;
> - goto out_cancel_attach;
> + if (tset->nr_tasks) {
> + do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> + if (ss->can_attach) {
> + tset->ssid = ssid;
> + ret = ss->can_attach(tset);
> + if (ret) {
> + failed_ssid = ssid;
> + goto out_cancel_attach;
> + }
> }
> - }
> - } while_each_subsys_mask();
> + } while_each_subsys_mask();
> + }
>
> /*
> * Now that we're guaranteed success, proceed to move all tasks to
> @@ -2085,25 +2089,29 @@ static int cgroup_migrate_execute(struct cgroup_mgctx
> *mgctx)
> */
> tset->csets = &tset->dst_csets;
>
> - do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> - if (ss->attach) {
> - tset->ssid = ssid;
> - ss->attach(tset);
> - }
> - } while_each_subsys_mask();
> + if (tset->nr_tasks) {
> + do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> + if (ss->attach) {
> + tset->ssid = ssid;
> + ss->attach(tset);
> + }
> + } while_each_subsys_mask();
> + }
>
> ret = 0;
> goto out_release_tset;
>
> out_cancel_attach:
> - do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> - if (ssid == failed_ssid)
> - break;
> - if (ss->cancel_attach) {
> - tset->ssid = ssid;
> - ss->cancel_attach(tset);
> - }
> - } while_each_subsys_mask();
> + if (tset->nr_tasks) {
> + do_each_subsys_mask(ss, ssid, mgctx->ss_mask) {
> + if (ssid == failed_ssid)
> + break;
> + if (ss->cancel_attach) {
> + tset->ssid = ssid;
> + ss->cancel_attach(tset);
> + }
> + } while_each_subsys_mask();
> + }
> out_release_tset:
> spin_lock_irq(&css_set_lock);
> list_splice_init(&tset->dst_csets, &tset->src_csets);
>
--
Regard's
Abdul Haleem
IBM Linux Technology Centre
