On Sun, Dec 27, 2020 at 10:43:44PM -0800, Hugh Dickins wrote: > On Sun, 27 Dec 2020, Linus Torvalds wrote: > > On Sun, Dec 27, 2020 at 3:48 PM Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> wrote: > > > > > > I did what Hugh proposed and it got clear to my eyes. It gets somewhat > > > large, but take a look. > > > > Ok, it's not that much bigger, and the end result is certainly much > > clearer wrt locking. > > > > So that last version of yours with the fix for the uninitialized 'ret' > > variable looks good to me. > > > > Of course, I've said that before, and have been wrong. So ... > > And guess what... it's broken. > > I folded it into testing rc1: segfault on cc1, systemd > "Journal file corrupted, rotating", seen on more than one machine. > > I've backed it out, rc1 itself seems fine, I'll leave rc1 under > load overnight, then come back to the faultaround patch tomorrow; > won't glance at it tonight, but maybe Kirill will guess what's wrong. 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. diff --git a/mm/filemap.c b/mm/filemap.c index c5da09f3f363..87671284de62 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2966,8 +2966,7 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, unsigned long address, mmap_miss--; vmf->address += (xas.xa_index - last_pgoff) << PAGE_SHIFT; - if (vmf->pte) - vmf->pte += xas.xa_index - last_pgoff; + vmf->pte += xas.xa_index - last_pgoff; last_pgoff = xas.xa_index; if (!pte_none(*vmf->pte)) diff --git a/mm/memory.c b/mm/memory.c index e51638b92e7c..829f5056dd1c 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -3785,13 +3785,16 @@ vm_fault_t finish_fault(struct vm_fault *vmf) vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, vmf->address, &vmf->ptl); + ret = 0; /* Re-check under ptl */ if (likely(pte_none(*vmf->pte))) do_set_pte(vmf, page); + else + ret = VM_FAULT_NOPAGE; update_mmu_tlb(vma, vmf->address, vmf->pte); pte_unmap_unlock(vmf->pte, vmf->ptl); - return 0; + return ret; } static unsigned long fault_around_bytes __read_mostly = -- Kirill A. Shutemov
