diff options
| author | Yafang Shao <laoar.shao@gmail.com> | 2023-10-29 06:14:31 +0000 |
|---|---|---|
| committer | Tejun Heo <tj@kernel.org> | 2023-11-09 13:25:47 -1000 |
| commit | 0008454e8fd30ed0017a9a35b8dd708f168931b8 (patch) | |
| tree | e1b0837749fe5823497f5206df8ebac983d1fe0d | |
| parent | 9067d90006df089b9a1da0d74f0cad232a5d726a (diff) | |
cgroup: Add annotation for holding namespace_sem in current_cgns_cgroup_from_root()
When I initially examined the function current_cgns_cgroup_from_root(), I
was perplexed by its lack of holding cgroup_mutex. However, after Michal
explained the reason[0] to me, I realized that it already holds the
namespace_sem. I believe this intricacy could also confuse others, so it
would be advisable to include an annotation for clarification.
After we replace the cgroup_mutex with RCU read lock, if current doesn't
hold the namespace_sem, the root cgroup will be NULL. So let's add a
WARN_ON_ONCE() for it.
[0]. https://lore.kernel.org/bpf/afdnpo3jz2ic2ampud7swd6so5carkilts2mkygcaw67vbw6yh@5b5mncf7qyet
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Cc: Michal Koutny <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
| -rw-r--r-- | kernel/cgroup/cgroup.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c index 9bb255e41cf2..4e610863cc37 100644 --- a/kernel/cgroup/cgroup.c +++ b/kernel/cgroup/cgroup.c @@ -1420,6 +1420,11 @@ current_cgns_cgroup_from_root(struct cgroup_root *root) rcu_read_unlock(); + /* + * The namespace_sem is held by current, so the root cgroup can't + * be umounted. Therefore, we can ensure that the res is non-NULL. + */ + WARN_ON_ONCE(!res); return res; } |