cgroup: Eliminate the need for cgroup_mutex in proc_cgroup_show()

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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>

...

This commit is contained in:

Yafang Shao 2023-10-29 06:14:30 +00:00 • committed by Tejun Heo

parent d23b5c5777

commit 9067d90006

1 changed files with 7 additions and 5 deletions

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kernel/cgroup/cgroup.c

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