On Mon, 22 May 2023, Qi Zheng wrote: > On 2023/5/22 12:54, Hugh Dickins wrote: > > filemap_map_pages() allow pte_offset_map_lock() to fail; and remove the > > pmd_devmap_trans_unstable() check from filemap_map_pmd(), which can safely > > return to filemap_map_pages() and let pte_offset_map_lock() discover that. > > > > Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx> > > --- > > mm/filemap.c | 12 +++++------- > > 1 file changed, 5 insertions(+), 7 deletions(-) > > > > diff --git a/mm/filemap.c b/mm/filemap.c > > index 28b42ee848a4..9e129ad43e0d 100644 > > --- a/mm/filemap.c > > +++ b/mm/filemap.c > > @@ -3408,13 +3408,6 @@ static bool filemap_map_pmd(struct vm_fault *vmf, > > struct folio *folio, > > if (pmd_none(*vmf->pmd)) > > pmd_install(mm, vmf->pmd, &vmf->prealloc_pte); > > - /* See comment in handle_pte_fault() */ > > - if (pmd_devmap_trans_unstable(vmf->pmd)) { > > - folio_unlock(folio); > > - folio_put(folio); > > - return true; > > - } > > - > > return false; > > } > > > > @@ -3501,6 +3494,11 @@ vm_fault_t filemap_map_pages(struct vm_fault *vmf, > > > > addr = vma->vm_start + ((start_pgoff - vma->vm_pgoff) << PAGE_SHIFT); > > vmf->pte = pte_offset_map_lock(vma->vm_mm, vmf->pmd, addr, &vmf->ptl); > > + if (!vmf->pte) { > > + folio_unlock(folio); > > + folio_put(folio); > > Missing: > ret = VM_FAULT_NOPAGE; > ? No, not missed. Here ret is 0, which leads do_read_fault() to try __do_fault() afterwards. Whereas VM_FAULT_NOPAGE would send it back to userspace to retry the whole fault. Either will work, but I think the intention of VM_FAULT_NOPAGE here in filemap_map_pages() is to say "the page you want is now inserted", which is probably not the case. Hugh