On Mon, Dec 28, 2020 at 10:47:36AM -0800, Linus Torvalds wrote: > On Mon, Dec 28, 2020 at 4:53 AM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > > > So far I only found one more pin leak and always-true check. I don't see > > how can it lead to crash or corruption. Keep looking. > > Well, I noticed that the nommu.c version of filemap_map_pages() needs > fixing, but that's obviously not the case Hugh sees. > > No,m I think the problem is the > > pte_unmap_unlock(vmf->pte, vmf->ptl); > > at the end of filemap_map_pages(). > > Why? > > Because we've been updating vmf->pte as we go along: > > vmf->pte += xas.xa_index - last_pgoff; > > and I think that by the time we get to that "pte_unmap_unlock()", > vmf->pte potentially points to past the edge of the page directory. Well, if it's true we have bigger problem: we set up an pte entry without relevant PTL. But I *think* we should be fine here: do_fault_around() limits start_pgoff and end_pgoff to stay within the page table. It made mw looking at the code around pte_unmap_unlock() and I think that the bug is that we have to reset vmf->address and NULLify vmf->pte once we are done with faultaround: diff --git a/mm/memory.c b/mm/memory.c index 829f5056dd1c..405f5c73ce3e 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3794,6 +3794,8 @@ vm_fault_t finish_fault(struct vm_fault *vmf) update_mmu_tlb(vma, vmf->address, vmf->pte); pte_unmap_unlock(vmf->pte, vmf->ptl); + vmf->address = address; + vmf->pte = NULL; return ret; } -- Kirill A. Shutemov
