The commit is pushed to "branch-rh9-5.14.vz9.1.x-ovz" and will appear at
https://src.openvz.org/scm/ovz/vzkernel.git
after rh9-5.14.0-4.vz9.10.1
------>
commit 90c3b81039abfa45f1037f86739a183374086912
Author: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
Date: Wed Oct 13 14:13:18 2021 +0300
cgroup: remove excess rcu_read_lock in cgroup marking
We do not need rcu_read_lock here because we are already protected by
ve->op_sem from ve->ve_ns modification, so let's simplify code.
Also remove excess warnings.
https://jira.sw.ru/browse/PSBM-134002
Fixes: 907c1e6cd67f ("cgroup: Mark cgroup CGRP_VE_ROOT")
Signed-off-by: Pavel Tikhomirov <ptikhomi...@virtuozzo.com>
---
kernel/cgroup/cgroup.c | 28 +++++++++++++++-------------
1 file changed, 15 insertions(+), 13 deletions(-)
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 05fe9436a9a3..a425f06eceea 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1969,19 +1969,20 @@ void cgroup_mark_ve_root(struct ve_struct *ve)
spin_lock_irq(&css_set_lock);
- rcu_read_lock();
- cset = rcu_dereference(ve->ve_ns)->cgroup_ns->root_cset;
- if (WARN_ON(!cset))
- goto unlock;
+ /*
+ * We can safely use ve->ve_ns without rcu_read_lock here, as we are
+ * always called _after_ ve_grab_context under ve->op_sem, so we've
+ * just set ve_ns and nobody else can modify it under us.
+ */
+ cset = rcu_dereference_protected(ve->ve_ns,
+ lockdep_is_held(&ve->op_sem))->cgroup_ns->root_cset;
list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
cgrp = link->cgrp;
set_bit(CGRP_VE_ROOT, &cgrp->flags);
}
- link_ve_root_cpu_cgroup(cset->subsys[cpu_cgrp_id]);
-unlock:
- rcu_read_unlock();
+ link_ve_root_cpu_cgroup(cset->subsys[cpu_cgrp_id]);
spin_unlock_irq(&css_set_lock);
}
@@ -1993,17 +1994,18 @@ void cgroup_unmark_ve_roots(struct ve_struct *ve)
spin_lock_irq(&css_set_lock);
- rcu_read_lock();
- cset = rcu_dereference(ve->ve_ns)->cgroup_ns->root_cset;
- if (WARN_ON(!cset))
- goto unlock;
+ /*
+ * We can safely use ve->ve_ns without rcu_read_lock here, as we are
+ * always called _before_ ve_drop_context under ve->op_sem, so we
+ * did not change ve_ns yet and nobody else can modify it under us.
+ */
+ cset = rcu_dereference_protected(ve->ve_ns,
+ lockdep_is_held(&ve->op_sem))->cgroup_ns->root_cset;
list_for_each_entry(link, &cset->cgrp_links, cgrp_link) {
cgrp = link->cgrp;
clear_bit(CGRP_VE_ROOT, &cgrp->flags);
}
-unlock:
- rcu_read_unlock();
spin_unlock_irq(&css_set_lock);
}
_______________________________________________
Devel mailing list
Devel@openvz.org
https://lists.openvz.org/mailman/listinfo/devel
