diff options
author | Yafang Shao <laoar.shao@gmail.com> | 2023-10-29 09:14:30 +0300 |
---|---|---|
committer | Tejun Heo <tj@kernel.org> | 2023-11-10 02:25:47 +0300 |
commit | 9067d90006df089b9a1da0d74f0cad232a5d726a (patch) | |
tree | f4e9faf68957ba9c800e8776b0840ffab66185e9 /kernel/cgroup/cgroup.c | |
parent | d23b5c577715892c87533b13923306acc6243f93 (diff) | |
download | linux-9067d90006df089b9a1da0d74f0cad232a5d726a.tar.xz |
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.c | 12 |
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; |