[Devel] [PATCH vz10 1/5] fixup! cgroup: use proper lockdep condition for ve_nsproxy dereference

[Eva Kurchatova]

From: Konstantin Khorenko <khorenko at virtuozzo.com>

cgroup_join_vz_slice() and cgroup_leave_vz_slice() dereference
ve->ve_nsproxy with rcu_dereference_protected(..., 1), which
unconditionally silences lockdep without naming the actual lock that
makes the access safe.

Both functions are only called from ve_start_container(), which runs
under ve->op_sem write-lock. The pointer is stable because
ve_grab_context() publishes it via rcu_assign_pointer() earlier in the
same function, and ve_drop_context() - the only path that clears it -
cannot run concurrently since it also requires op_sem.

Replace the unconditional "1" with lockdep_is_held(&ve->op_sem) so
that lockdep can actually verify the locking at runtime. This is
consistent with how ve_grab_context(), ve_drop_context(), and
ve_stop_ns() already annotate the same pointer.

Fixes: f74e12f9f249a ("ve/cgroup: add vz.slice cgroup to put kernel threads to")
https://virtuozzo.atlassian.net/browse/VSTOR-128317

Feature: ve: ve generic structures
Signed-off-by: Konstantin Khorenko <khorenko at virtuozzo.com>
---
 kernel/cgroup/cgroup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 5585545304a3..0bd3aff89dbd 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -2252,7 +2252,8 @@ int cgroup_join_vz_slice(struct ve_struct *ve)
 	struct cgroup *cgrp;
 	int ret;
 
-	cset = rcu_dereference_protected(ve->ve_nsproxy, 1)->cgroup_ns->root_cset;
+	cset = rcu_dereference_protected(ve->ve_nsproxy,
+				lockdep_is_held(&ve->op_sem))->cgroup_ns->root_cset;
 	cgrp = __cset_cgroup_from_root(cset, &cgrp_dfl_root);
 
 	if (!is_virtualized_cgroup(cgrp) ||
@@ -2287,7 +2288,8 @@ int cgroup_leave_vz_slice(struct ve_struct *ve)
 	struct css_set *cset;
 	struct cgroup *cgrp;
 
-	cset = rcu_dereference_protected(ve->ve_nsproxy, 1)->cgroup_ns->root_cset;
+	cset = rcu_dereference_protected(ve->ve_nsproxy,
+				lockdep_is_held(&ve->op_sem))->cgroup_ns->root_cset;
 	cgrp = __cset_cgroup_from_root(cset, &cgrp_dfl_root);
 
 	if (!is_virtualized_cgroup(cgrp) ||
-- 
2.54.0