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.

Fixes: 5d317b2b6536 ("mm: hugetlb: proc: add HugetlbPages field to /proc/PID/status") Signed-off-by: Liu Zixian liuzixian4@huawei.com --- v2: 1. Create two hugetlb_count_init in hugetlb.h instead of using #ifdef in fork.c 2. Add an example to clearify this issue. --- include/linux/hugetlb.h | 9 +++++++++ kernel/fork.c | 1 + 2 files changed, 10 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index f7ca1a387..1faebe1cd 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -858,6 +858,11 @@ static inline spinlock_t *huge_pte_lockptr(struct hstate *h,

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_lockptr(struct hstate *h, 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) { } diff --git a/kernel/fork.c b/kernel/fork.c index bc94b2cc5..0dbc96ade 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1050,6 +1050,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p, 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;