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-rw-r--r--mm/memcontrol.c19
1 files changed, 9 insertions, 10 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 7a22b41..00bb8a6 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1925,19 +1925,18 @@ again:
rcu_read_lock();
p = rcu_dereference(mm->owner);
- VM_BUG_ON(!p);
/*
- * because we don't have task_lock(), "p" can exit while
- * we're here. In that case, "mem" can point to root
- * cgroup but never be NULL. (and task_struct itself is freed
- * by RCU, cgroup itself is RCU safe.) Then, we have small
- * risk here to get wrong cgroup. But such kind of mis-account
- * by race always happens because we don't have cgroup_mutex().
- * It's overkill and we allow that small race, here.
+ * Because we don't have task_lock(), "p" can exit.
+ * In that case, "mem" can point to root or p can be NULL with
+ * race with swapoff. Then, we have small risk of mis-accouning.
+ * But such kind of mis-account by race always happens because
+ * we don't have cgroup_mutex(). It's overkill and we allo that
+ * small race, here.
+ * (*) swapoff at el will charge against mm-struct not against
+ * task-struct. So, mm->owner can be NULL.
*/
mem = mem_cgroup_from_task(p);
- VM_BUG_ON(!mem);
- if (mem_cgroup_is_root(mem)) {
+ if (!mem || mem_cgroup_is_root(mem)) {
rcu_read_unlock();
goto done;
}
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