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    SubjectRe: [PATCH v4 49/66] bpf: Remove VMA linked list
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    On 12/1/21 15:30, Liam Howlett wrote:
    > From: "Liam R. Howlett" <Liam.Howlett@Oracle.com>
    >
    > Use vma_next() and remove reference to the start of the linked list
    >
    > Signed-off-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
    > ---
    > kernel/bpf/task_iter.c | 21 ++++-----------------
    > 1 file changed, 4 insertions(+), 17 deletions(-)
    >
    > diff --git a/kernel/bpf/task_iter.c b/kernel/bpf/task_iter.c
    > index b48750bfba5a..2d964743f1e6 100644
    > --- a/kernel/bpf/task_iter.c
    > +++ b/kernel/bpf/task_iter.c
    > @@ -299,8 +299,8 @@ struct bpf_iter_seq_task_vma_info {
    > };
    >
    > enum bpf_task_vma_iter_find_op {
    > - task_vma_iter_first_vma, /* use mm->mmap */
    > - task_vma_iter_next_vma, /* use curr_vma->vm_next */
    > + task_vma_iter_first_vma, /* use find_vma() with addr 0 */
    > + task_vma_iter_next_vma, /* use vma_next() with curr_vma */
    > task_vma_iter_find_vma, /* use find_vma() to find next vma */
    > };
    >
    > @@ -400,24 +400,11 @@ task_vma_seq_get_next(struct bpf_iter_seq_task_vma_info *info)
    >
    > switch (op) {
    > case task_vma_iter_first_vma:
    > - curr_vma = curr_task->mm->mmap;
    > + curr_vma = find_vma(curr_task->mm, 0);
    > break;
    > case task_vma_iter_next_vma:
    > - curr_vma = curr_vma->vm_next;
    > - break;
    > case task_vma_iter_find_vma:
    > - /* We dropped mmap_lock so it is necessary to use find_vma
    > - * to find the next vma. This is similar to the mechanism
    > - * in show_smaps_rollup().
    > - */
    > - curr_vma = find_vma(curr_task->mm, info->prev_vm_end - 1);
    > - /* case 1) and 4.2) above just use curr_vma */
    > -
    > - /* check for case 2) or case 4.1) above */
    > - if (curr_vma &&
    > - curr_vma->vm_start == info->prev_vm_start &&
    > - curr_vma->vm_end == info->prev_vm_end)
    > - curr_vma = curr_vma->vm_next;
    > + curr_vma = find_vma(curr_task->mm, curr_vma->vm_end);

    Are you sure curr_vma is valid here and we can read its vm_end? Because I
    have no idea, but lots of doubts.

    > break;
    > }
    > if (!curr_vma) {

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