Commit 479adb89 authored by Tejun Heo's avatar Tejun Heo
Browse files

cgroup: Fix dom_cgrp propagation when enabling threaded mode 



A cgroup which is already a threaded domain may be converted into a
threaded cgroup if the prerequisite conditions are met.  When this
happens, all threaded descendant should also have their ->dom_cgrp
updated to the new threaded domain cgroup.  Unfortunately, this
propagation was missing leading to the following failure.

  # cd /sys/fs/cgroup/unified
  # cat cgroup.subtree_control    # show that no controllers are enabled

  # mkdir -p mycgrp/a/b/c
  # echo threaded > mycgrp/a/b/cgroup.type

  At this point, the hierarchy looks as follows:

      mycgrp [d]
	  a [dt]
	      b [t]
		  c [inv]

  Now let's make node "a" threaded (and thus "mycgrp" s made "domain threaded"):

  # echo threaded > mycgrp/a/cgroup.type

  By this point, we now have a hierarchy that looks as follows:

      mycgrp [dt]
	  a [t]
	      b [t]
		  c [inv]

  But, when we try to convert the node "c" from "domain invalid" to
  "threaded", we get ENOTSUP on the write():

  # echo threaded > mycgrp/a/b/c/cgroup.type
  sh: echo: write error: Operation not supported

This patch fixes the problem by

* Moving the opencoded ->dom_cgrp save and restoration in
  cgroup_enable_threaded() into cgroup_{save|restore}_control() so
  that mulitple cgroups can be handled.

* Updating all threaded descendants' ->dom_cgrp to point to the new
  dom_cgrp when enabling threaded mode.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Reported-and-tested-by: default avatar"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>
Reported-by: default avatarAmin Jamali <ajamali@pivotal.io>
Reported-by: default avatarJoao De Almeida Pereira <jpereira@pivotal.io>
Link: https://lore.kernel.org/r/CAKgNAkhHYCMn74TCNiMJ=ccLd7DcmXSbvw3CbZ1YREeG7iJM5g@mail.gmail.com
Fixes: 454000ad ("cgroup: introduce cgroup->dom_cgrp and threaded css_set handling")
Cc: stable@vger.kernel.org # v4.14+
parent ac0657ed

include/linux/cgroup-defs.h

+1 −0
Original line number Diff line number Diff line
@@ -412,6 +412,7 @@ struct cgroup { 
	 * specific task are charged to the dom_cgrp.

	 */

	struct cgroup *dom_cgrp;

	struct cgroup *old_dom_cgrp;		/* used while enabling threaded */



	/* per-cpu recursive resource statistics */

	struct cgroup_rstat_cpu __percpu *rstat_cpu;

kernel/cgroup/cgroup.c

+16 −9
Original line number Diff line number Diff line
@@ -2836,11 +2836,12 @@ restart: 
}



/**

 * cgroup_save_control - save control masks of a subtree

 * cgroup_save_control - save control masks and dom_cgrp of a subtree

 * @cgrp: root of the target subtree

 *

 * Save ->subtree_control and ->subtree_ss_mask to the respective old_

 * prefixed fields for @cgrp's subtree including @cgrp itself.

 * Save ->subtree_control, ->subtree_ss_mask and ->dom_cgrp to the

 * respective old_ prefixed fields for @cgrp's subtree including @cgrp

 * itself.

 */

static void cgroup_save_control(struct cgroup *cgrp)

{
@@ -2850,6 +2851,7 @@ static void cgroup_save_control(struct cgroup *cgrp) 
	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp) {

		dsct->old_subtree_control = dsct->subtree_control;

		dsct->old_subtree_ss_mask = dsct->subtree_ss_mask;

		dsct->old_dom_cgrp = dsct->dom_cgrp;

	}

}
@@ -2875,11 +2877,12 @@ static void cgroup_propagate_control(struct cgroup *cgrp) 
}



/**

 * cgroup_restore_control - restore control masks of a subtree

 * cgroup_restore_control - restore control masks and dom_cgrp of a subtree

 * @cgrp: root of the target subtree

 *

 * Restore ->subtree_control and ->subtree_ss_mask from the respective old_

 * prefixed fields for @cgrp's subtree including @cgrp itself.

 * Restore ->subtree_control, ->subtree_ss_mask and ->dom_cgrp from the

 * respective old_ prefixed fields for @cgrp's subtree including @cgrp

 * itself.

 */

static void cgroup_restore_control(struct cgroup *cgrp)

{
@@ -2889,6 +2892,7 @@ static void cgroup_restore_control(struct cgroup *cgrp) 
	cgroup_for_each_live_descendant_post(dsct, d_css, cgrp) {

		dsct->subtree_control = dsct->old_subtree_control;

		dsct->subtree_ss_mask = dsct->old_subtree_ss_mask;

		dsct->dom_cgrp = dsct->old_dom_cgrp;

	}

}
@@ -3196,6 +3200,8 @@ static int cgroup_enable_threaded(struct cgroup *cgrp) 
{

	struct cgroup *parent = cgroup_parent(cgrp);

	struct cgroup *dom_cgrp = parent->dom_cgrp;

	struct cgroup *dsct;

	struct cgroup_subsys_state *d_css;

	int ret;



	lockdep_assert_held(&cgroup_mutex);
@@ -3225,12 +3231,13 @@ static int cgroup_enable_threaded(struct cgroup *cgrp) 
	 */

	cgroup_save_control(cgrp);



	cgrp->dom_cgrp = dom_cgrp;

	cgroup_for_each_live_descendant_pre(dsct, d_css, cgrp)

		if (dsct == cgrp || cgroup_is_threaded(dsct))

			dsct->dom_cgrp = dom_cgrp;



	ret = cgroup_apply_control(cgrp);

	if (!ret)

		parent->nr_threaded_children++;

	else

		cgrp->dom_cgrp = cgrp;



	cgroup_finalize_control(cgrp, ret);

	return ret;

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