On Wed, 17 May 2023 15:09:15 -0400 Peter Xu <peterx@xxxxxxxxxx> wrote: > It seems vma merging with uffd paths is broken with either > register/unregister, where right now we can feed wrong parameters to > vma_merge() and it's found by recent patch which moved asserts upwards in > vma_merge() by Lorenzo Stoakes: > > https://lore.kernel.org/all/ZFunF7DmMdK05MoF@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/ > > It's possible that "start" is contained within vma but not clamped to its > start. We need to convert this into either "cannot merge" case or "can > merge" case 4 which permits subdivision of prev by assigning vma to > prev. As we loop, each subsequent VMA will be clamped to the start. > > This patch will eliminate the report and make sure vma_merge() calls will > become legal again. > > One thing to mention is that the "Fixes: 29417d292bd0" below is there only > to help explain where the warning can start to trigger, the real commit to > fix should be 69dbe6daf104. Commit 29417d292bd0 helps us to identify the > issue, but unfortunately we may want to keep it in Fixes too just to ease > kernel backporters for easier tracking. > > Cc: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx> > Cc: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > Reported-by: Mark Rutland <mark.rutland@xxxxxxx> > Reviewed-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> > Reviewed-by: Liam R. Howlett <Liam.Howlett@xxxxxxxxxx> > Fixes: 29417d292bd0 ("mm/mmap/vma_merge: always check invariants") > Fixes: 69dbe6daf104 ("userfaultfd: use maple tree iterator to iterate VMAs") I don't know how -stable maintainers are to handle more than a single Fixes: target, given that Fixes: means "kernels which have that patch need this one". Can we narrow this down to a single commit for this purpose?
