[PATCH 5.14 406/432] mm/hugetlb: initialize hugetlb_usage in mm_init

Greg Kroah-Hartman
2021-09-16T17:52:05Z

From: Liu Zixian <liuzixian4@huawei.com>

commit 13db8c50477d83ad3e3b9b0ae247e5cd833a7ae4 upstream.

After fork, the child process will get incorrect (2x) hugetlb_usage. If
a process uses 5 2MB hugetlb pages in an anonymous mapping,

HugetlbPages: 10240 kB

and then forks, the child will show,

HugetlbPages: 20480 kB

The reason for double the amount is because hugetlb_usage will be copied
from the parent and then increased when we copy page tables from parent
to child. Child will have 2x actual usage.

Fix this by adding hugetlb_count_init in mm_init.

Link: https://lkml.kernel.org/r/20210826071742.877-1-liuzixian4@huawei.com
Fixes: 5d317b2b6536 ("mm: hugetlb: proc: add HugetlbPages field to /proc/PID/status")
Signed-off-by: Liu Zixian <liuzixian4@huawei.com>
Reviewed-by: Naoya Horiguchi <naoya.horiguchi@nec.com>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/linux/hugetlb.h | 9 +++++++++
kernel/fork.c | 1 +
2 files changed, 10 insertions(+)

--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -858,6 +858,11 @@ static inline spinlock_t *huge_pte_lockp

void hugetlb_report_usage(struct seq_file *m, struct mm_struct *mm);

+static inline void hugetlb_count_init(struct mm_struct *mm)
+{
+ atomic_long_set(&mm->hugetlb_usage, 0);
+}
+
static inline void hugetlb_count_add(long l, struct mm_struct *mm)
{
atomic_long_add(l, &mm->hugetlb_usage);
@@ -1042,6 +1047,10 @@ static inline spinlock_t *huge_pte_lockp
return &mm->page_table_lock;
}

+static inline void hugetlb_count_init(struct mm_struct *mm)
+{
+}
+
static inline void hugetlb_report_usage(struct seq_file *f, struct mm_struct *m)
{
}
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1050,6 +1050,7 @@ static struct mm_struct *mm_init(struct
mm->pmd_huge_pte = NULL;
#endif
mm_init_uprobes_state(mm);
+ hugetlb_count_init(mm);

if (current->mm) {
mm->flags = current->mm->flags & MMF_INIT_MASK;