Re: [PATCH v6 7/8] fs/proc/task_mmu: read proc/pid/maps under per-vma lock

On Wed, Jul 9, 2025 at 3:03 AM Vlastimil Babka vbabka@suse.cz wrote:

On 7/4/25 08:07, Suren Baghdasaryan wrote:

...

--- a/mm/mmap_lock.c +++ b/mm/mmap_lock.c @@ -178,6 +178,94 @@ struct vm_area_struct *lock_vma_under_rcu(struct mm_struct *mm, count_vm_vma_lock_event(VMA_LOCK_ABORT); return NULL; }

+static struct vm_area_struct *lock_vma_under_mmap_lock(struct mm_struct *mm,

•                                                struct vma_iterator *iter,
  

•                                                unsigned long address)
  

+{

• struct vm_area_struct *vma;
  

• int ret;
  

• ret = mmap_read_lock_killable(mm);
  

• if (ret)
  

•         return ERR_PTR(ret);
  

• /* Lookup the vma at the last position again under mmap_read_lock */
  

• vma_iter_init(iter, mm, address);
  

• vma = vma_next(iter);
  

• if (vma)
  

•         vma_start_read_locked(vma);
  

This can in theory return false (refcount overflow?) so it should be handled?

Yes, I should handle it by falling back to mmap_lock. Thanks!

...

• mmap_read_unlock(mm);
  

• return vma;
  

+}