[Devel] [PATCH RHEL10 COMMIT] mm: fix negative dentry accounting by protecting memcg with rcu_read_lock

[Konstantin Khorenko]

The commit is pushed to "branch-rh10-6.12.0-55.13.1.vz10.2.x-ovz" and will appear at git at bitbucket.org:openvz/vzkernel.git
after rh10-6.12.0-55.13.1.el10
------>
commit 333f254f205b2bd67140f3923806347af62f66cb
Author: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
Date:   Mon Aug 4 11:29:48 2025 +0800

    mm: fix negative dentry accounting by protecting memcg with rcu_read_lock
    
    This fixes the warning:
    
    WARNING: CPU: 0 PID: 1 at include/linux/memcontrol.h:404 mem_cgroup_from_slab_obj+0x426/0x580
    
    In this stack:
    
      +-> dput
        +-> __dentry_kill
          +-> d_lru_del
            +-> memcg_neg_dentry_dec
              +-> mem_cgroup_from_slab_obj
                +-> mem_cgroup_from_obj_folio
                  +-> obj_cgroup_memcg
    
    Detected when running xfstests-generic/321.
    
    https://virtuozzo.atlassian.net/browse/VSTOR-112802
    Fixes: 2b4edb1f998a ("mm: per-memcg negative dentries accounting")
    Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
    
    Feature: mm: statistic enhancements
---
 mm/memcontrol.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 175d43481c6f2..3563586ff93fd 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -3240,18 +3240,24 @@ unsigned long mem_cgroup_read_nd(struct mem_cgroup *memcg)
 
 void memcg_neg_dentry_inc(struct dentry *dentry)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_slab_obj(dentry);
+	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+	memcg = mem_cgroup_from_slab_obj(dentry);
 	if (memcg)
 		__this_cpu_inc(memcg->vmstats_percpu->nr_dentry_neg);
+	rcu_read_unlock();
 }
 
 void memcg_neg_dentry_dec(struct dentry *dentry)
 {
-	struct mem_cgroup *memcg = mem_cgroup_from_slab_obj(dentry);
+	struct mem_cgroup *memcg;
 
+	rcu_read_lock();
+	memcg = mem_cgroup_from_slab_obj(dentry);
 	if (memcg)
 		__this_cpu_dec(memcg->vmstats_percpu->nr_dentry_neg);
+	rcu_read_unlock();
 }
 
 /*