On Tue, Jun 04, 2024 at 05:24:46PM -0700, Andrii Nakryiko wrote:
> +/*
> + * find_and_lock_vma_rcu() - Find and lock the VMA for a given address, or the
> + * next VMA. Search is done under RCU protection, without taking or assuming
> + * mmap_lock. Returned VMA is guaranteed to be stable and not isolated.
You know this is supposed to be the _short_ description, right?
Three lines is way too long. The full description goes between the
arguments and the Return: line.
> + * @mm: The mm_struct to check
> + * @addr: The address
> + *
> + * Returns: The VMA associated with addr, or the next VMA.
> + * May return %NULL in the case of no VMA at addr or above.
> + * If the VMA is being modified and can't be locked, -EBUSY is returned.
> + */
> +struct vm_area_struct *find_and_lock_vma_rcu(struct mm_struct *mm,
> + unsigned long address)
> +{
> + MA_STATE(mas, &mm->mm_mt, address, address);
> + struct vm_area_struct *vma;
> + int err;
> +
> + rcu_read_lock();
> +retry:
> + vma = mas_find(&mas, ULONG_MAX);
> + if (!vma) {
> + err = 0; /* no VMA, return NULL */
> + goto inval;
> + }
> +
> + if (!vma_start_read(vma)) {
> + err = -EBUSY;
> + goto inval;
> + }
> +
> + /*
> + * Check since vm_start/vm_end might change before we lock the VMA.
> + * Note, unlike lock_vma_under_rcu() we are searching for VMA covering
> + * address or the next one, so we only make sure VMA wasn't updated to
> + * end before the address.
> + */
> + if (unlikely(vma->vm_end <= address)) {
> + err = -EBUSY;
> + goto inval_end_read;
> + }
> +
> + /* Check if the VMA got isolated after we found it */
> + if (vma->detached) {
> + vma_end_read(vma);
> + count_vm_vma_lock_event(VMA_LOCK_MISS);
> + /* The area was replaced with another one */
Surely you need to mas_reset() before you goto retry?
> + goto retry;
> + }
