4.18-stable review patch. If anyone has any objections, please let me know.
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From: Tejun Heo tj@kernel.org
commit 479adb89a97b0a33e5a9d702119872cc82ca21aa upstream.
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: Tejun Heo tj@kernel.org Reported-and-tested-by: "Michael Kerrisk (man-pages)" mtk.manpages@gmail.com Reported-by: Amin Jamali ajamali@pivotal.io Reported-by: Joao De Almeida Pereira jpereira@pivotal.io Link: https://lore.kernel.org/r/CAKgNAkhHYCMn74TCNiMJ=ccLd7DcmXSbvw3CbZ1YREeG7iJM5... Fixes: 454000adaa2a ("cgroup: introduce cgroup->dom_cgrp and threaded css_set handling") Cc: stable@vger.kernel.org # v4.14+ Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- include/linux/cgroup-defs.h | 1 + kernel/cgroup/cgroup.c | 25 ++++++++++++++++--------- 2 files changed, 17 insertions(+), 9 deletions(-)
--- a/include/linux/cgroup-defs.h +++ b/include/linux/cgroup-defs.h @@ -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; --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -2833,11 +2833,12 @@ 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) { @@ -2847,6 +2848,7 @@ static void cgroup_save_control(struct c 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; } }
@@ -2872,11 +2874,12 @@ static void cgroup_propagate_control(str }
/** - * 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) { @@ -2886,6 +2889,7 @@ static void cgroup_restore_control(struc 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; } }
@@ -3193,6 +3197,8 @@ static int cgroup_enable_threaded(struct { 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); @@ -3222,12 +3228,13 @@ static int cgroup_enable_threaded(struct */ 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;