Commit 0008454e authored by Yafang Shao's avatar Yafang Shao Committed by Tejun Heo
Browse files

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: default avatarYafang Shao <laoar.shao@gmail.com>
Cc: Michal Koutny <mkoutny@suse.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 9067d900

kernel/cgroup/cgroup.c

+5 −0
Original line number Diff line number Diff line
@@ -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;

}