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    Subject[PATCH 3/4] mm: Fix some minor per-VMA lock issues in userfaultfd
    Date
    Rename lock_vma() to uffd_lock_vma() because it really is uffd specific.
    Remove comment referencing unlock_vma() which doesn't exist.
    Fix the comment about lock_vma_under_rcu() which I just made incorrect.

    Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    ---
    mm/userfaultfd.c | 20 +++++++++-----------
    1 file changed, 9 insertions(+), 11 deletions(-)

    diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
    index e6486923263c..defa5109cc62 100644
    --- a/mm/userfaultfd.c
    +++ b/mm/userfaultfd.c
    @@ -56,17 +56,16 @@ struct vm_area_struct *find_vma_and_prepare_anon(struct mm_struct *mm,

    #ifdef CONFIG_PER_VMA_LOCK
    /*
    - * lock_vma() - Lookup and lock vma corresponding to @address.
    + * uffd_lock_vma() - Lookup and lock vma corresponding to @address.
    * @mm: mm to search vma in.
    * @address: address that the vma should contain.
    *
    - * Should be called without holding mmap_lock. vma should be unlocked after use
    - * with unlock_vma().
    + * Should be called without holding mmap_lock.
    *
    * Return: A locked vma containing @address, -ENOENT if no vma is found, or
    * -ENOMEM if anon_vma couldn't be allocated.
    */
    -static struct vm_area_struct *lock_vma(struct mm_struct *mm,
    +static struct vm_area_struct *uffd_lock_vma(struct mm_struct *mm,
    unsigned long address)
    {
    struct vm_area_struct *vma;
    @@ -74,9 +73,8 @@ static struct vm_area_struct *lock_vma(struct mm_struct *mm,
    vma = lock_vma_under_rcu(mm, address);
    if (vma) {
    /*
    - * lock_vma_under_rcu() only checks anon_vma for private
    - * anonymous mappings. But we need to ensure it is assigned in
    - * private file-backed vmas as well.
    + * We know we're going to need to use anon_vma, so check
    + * that early.
    */
    if (!(vma->vm_flags & VM_SHARED) && unlikely(!vma->anon_vma))
    vma_end_read(vma);
    @@ -107,7 +105,7 @@ static struct vm_area_struct *uffd_mfill_lock(struct mm_struct *dst_mm,
    {
    struct vm_area_struct *dst_vma;

    - dst_vma = lock_vma(dst_mm, dst_start);
    + dst_vma = uffd_lock_vma(dst_mm, dst_start);
    if (IS_ERR(dst_vma) || validate_dst_vma(dst_vma, dst_start + len))
    return dst_vma;

    @@ -1436,7 +1434,7 @@ static int uffd_move_lock(struct mm_struct *mm,
    struct vm_area_struct *vma;
    int err;

    - vma = lock_vma(mm, dst_start);
    + vma = uffd_lock_vma(mm, dst_start);
    if (IS_ERR(vma))
    return PTR_ERR(vma);

    @@ -1451,7 +1449,7 @@ static int uffd_move_lock(struct mm_struct *mm,
    }

    /*
    - * Using lock_vma() to get src_vma can lead to following deadlock:
    + * Using uffd_lock_vma() to get src_vma can lead to following deadlock:
    *
    * Thread1 Thread2
    * ------- -------
    @@ -1473,7 +1471,7 @@ static int uffd_move_lock(struct mm_struct *mm,
    err = find_vmas_mm_locked(mm, dst_start, src_start, dst_vmap, src_vmap);
    if (!err) {
    /*
    - * See comment in lock_vma() as to why not using
    + * See comment in uffd_lock_vma() as to why not using
    * vma_start_read() here.
    */
    down_read(&(*dst_vmap)->vm_lock->lock);
    --
    2.43.0

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