* Vlastimil Babka <vbabka@xxxxxxx> [220119 12:05]:
> On 12/1/21 15:30, Liam Howlett wrote:
> > From: "Liam R. Howlett" <Liam.Howlett@xxxxxxxxxx>
> >
> > Use vma_next() and remove reference to the start of the linked list
> >
> > Signed-off-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx>
> > ---
> > 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.
I am not sure. I'm going to drop this patch and take the more
conservative but safer v3 version.
>
> > break;
> > }
> > if (!curr_vma) {
>
>
