| Message ID | 3e6d4f8-9f4d-fa7e-304e-1494dddd45b@google.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | mm: allow pte_offset_map[_lock]() to fail | expand |
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@google.com> > --- > 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; ? > + goto out; > + } > do { > again: > page = folio_file_page(folio, xas.xa_index);
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@google.com> > > --- > > 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
On 2023/5/24 10:35, Hugh Dickins wrote: > 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@google.com> >>> --- >>> 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. Got it. Thanks for the explanation. > > Hugh
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); + goto out; + } do { again: page = folio_file_page(folio, xas.xa_index);
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@google.com> --- mm/filemap.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)