summaryrefslogtreecommitdiff
path: root/kernel/cgroup/cgroup.c
diff options
context:
space:
mode:
authorYafang Shao <laoar.shao@gmail.com>2023-10-29 06:14:30 +0000
committerTejun Heo <tj@kernel.org>2023-11-09 13:25:47 -1000
commit9067d90006df089b9a1da0d74f0cad232a5d726a (patch)
treef4e9faf68957ba9c800e8776b0840ffab66185e9 /kernel/cgroup/cgroup.c
parentd23b5c577715892c87533b13923306acc6243f93 (diff)
cgroup: Eliminate the need for cgroup_mutex in proc_cgroup_show()
The cgroup root_list is already RCU-safe. Therefore, we can replace the cgroup_mutex with the RCU read lock in some particular paths. This change will be particularly beneficial for frequent operations, such as `cat /proc/self/cgroup`, in a cgroup1-based container environment. I did stress tests with this change, as outlined below (with CONFIG_PROVE_RCU_LIST enabled): - Continuously mounting and unmounting named cgroups in some tasks, for example: cgrp_name=$1 while true do mount -t cgroup -o none,name=$cgrp_name none /$cgrp_name umount /$cgrp_name done - Continuously triggering proc_cgroup_show() in some tasks concurrently, for example: while true; do cat /proc/self/cgroup > /dev/null; done They can ran successfully after implementing this change, with no RCU warnings in dmesg. Signed-off-by: Yafang Shao <laoar.shao@gmail.com> Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/cgroup/cgroup.c')
-rw-r--r--kernel/cgroup/cgroup.c12
1 files changed, 7 insertions, 5 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 19784d44d615..9bb255e41cf2 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -6285,7 +6285,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
if (!buf)
goto out;
- cgroup_lock();
+ rcu_read_lock();
spin_lock_irq(&css_set_lock);
for_each_root(root) {
@@ -6296,6 +6296,11 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
if (root == &cgrp_dfl_root && !READ_ONCE(cgrp_dfl_visible))
continue;
+ cgrp = task_cgroup_from_root(tsk, root);
+ /* The root has already been unmounted. */
+ if (!cgrp)
+ continue;
+
seq_printf(m, "%d:", root->hierarchy_id);
if (root != &cgrp_dfl_root)
for_each_subsys(ss, ssid)
@@ -6306,9 +6311,6 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
seq_printf(m, "%sname=%s", count ? "," : "",
root->name);
seq_putc(m, ':');
-
- cgrp = task_cgroup_from_root(tsk, root);
-
/*
* On traditional hierarchies, all zombie tasks show up as
* belonging to the root cgroup. On the default hierarchy,
@@ -6340,7 +6342,7 @@ int proc_cgroup_show(struct seq_file *m, struct pid_namespace *ns,
retval = 0;
out_unlock:
spin_unlock_irq(&css_set_lock);
- cgroup_unlock();
+ rcu_read_unlock();
kfree(buf);
out:
return retval;