> > Since copy_vma_and_data() which calls copy_vma() intends to reference the > old VMA after the merge, it must have this pointer updated. > > This kind of self-merge is not possible with a succeeding merge, as the > merge always prefers to expand the preceding VMA if possible. > > copy_vma() accounts for this by explicitly checking to see if a self-merge > occurred and updating the vmap pointer if so. However it incorrect did so > even for a subsequent merge (this is simply a noop so it had no impact).
Took me longer than it should to find out that this is no real fix ;) > > So change this to only check for the case which matters - a backwards > merge - and rearrange the parameters to make it clearer we're doing that - > i.e. check new_vma->vm_start < old_vma_start (having already renamed > vma_start to old_vma_start to make it clear this is the previous VMA). > > Also update the existing wall-of-text comment to be a lot clearer. > > While we're here, replace the VM_BUG_ON_VMA() with a VM_WARN_ON_ONCE_VMA() > and update the VMA userland tests accordingly. > > No functional change intended. > > Signed-off-by: Lorenzo Stoakes (ARM) <[email protected]> > --- I skimmed over it, looks correct, but the merging stuff is way over my head to confidentially give a RB tag her :) -- Cheers, David
