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    Subject[PATCH 4.14 188/217] mm/hugetlb: initialize hugetlb_usage in mm_init
    Date
    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
    @@ -503,6 +503,11 @@ 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);
    @@ -583,6 +588,10 @@ 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
    @@ -837,6 +837,7 @@ 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;

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