* Matthew Wilcox <willy@xxxxxxxxxxxxx> [240604 20:57]:
> 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?
Probably more than that. We've found and may have adjusted the
index/last; we should reconfigure the maple state. You should probably
use mas_set(), which will reset the maple state and set the index and
long to address.
>
> > + goto retry;
> > + }
>
