docs/cgroup: add entry for cgroup.kill

Give a brief overview of the cgroup.kill functionality.

Link: https://lore.kernel.org/r/20210503143922.3093755-2-brauner@kernel.org
Cc: Roman Gushchin <guro@fb.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: cgroups@vger.kernel.org
Reviewed-by: Shakeel Butt <shakeelb@google.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
index b1e81aa..91cd601 100644 (file)
--- a/Documentation/admin-guide/cgroup-v2.rst
+++ b/Documentation/admin-guide/cgroup-v2.rst
@@ -952,6 +952,21 @@ All cgroup core files are prefixed with "cgroup."
        it's possible to delete a frozen (and empty) cgroup, as well as
        create new sub-cgroups.
 
+  cgroup.kill
+       A write-only single value file which exists in non-root cgroups.
+       The only allowed value is "1".
+
+       Writing "1" to the file causes the cgroup and all descendant cgroups to
+       be killed. This means that all processes located in the affected cgroup
+       tree will be killed via SIGKILL.
+
+       Killing a cgroup tree will deal with concurrent forks appropriately and
+       is protected against migrations.
+
+       In a threaded cgroup, writing this file fails with EOPNOTSUPP as
+       killing cgroups is a process directed operation, i.e. it affects
+       the whole thread-group.
+
 Controllers
 ===========