Re: generic/068 crash on 5.18-rc2?

[Matthew Wilcox <willy@infradead.org>]

On Sat, Apr 30, 2022 at 04:44:07AM +0100, Matthew Wilcox wrote:
> (I do not love this, have not even compiled it; it's late.  We may be
> better off just storing next_folio inside the folio_iter).

Does anyone have a preference for fixing this between Option A:

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 49eff01fb829..55e2499beff6 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -269,6 +269,7 @@ struct folio_iter {
        size_t offset;
        size_t length;
        /* private: for use by the iterator */
+       struct folio *_next;
        size_t _seg_count;
        int _i;
 };
@@ -280,19 +281,23 @@ static inline void bio_first_folio(struct folio_iter *fi,
struct bio *bio,

        fi->folio = page_folio(bvec->bv_page);
        fi->offset = bvec->bv_offset +
-                       PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
+                       PAGE_SIZE * folio_page_idx(fi->folio, bvec->bv_page);
        fi->_seg_count = bvec->bv_len;
        fi->length = min(folio_size(fi->folio) - fi->offset, fi->_seg_count);
        fi->_i = i;
+       if (fi->_seg_count > fi->length)
+               fi->_next = folio_next(fi->folio);
 }

 static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
 {
        fi->_seg_count -= fi->length;
        if (fi->_seg_count) {
-               fi->folio = folio_next(fi->folio);
+               fi->folio = fi->_next;
                fi->offset = 0;
                fi->length = min(folio_size(fi->folio), fi->_seg_count);
+               if (fi->_seg_count > fi->length)
+                       fi->_next = folio_next(fi->folio);
        } else if (fi->_i + 1 < bio->bi_vcnt) {
                bio_first_folio(fi, bio, fi->_i + 1);
        } else {


and Option B:

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 49eff01fb829..554f5fce060c 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -290,7 +290,8 @@ static inline void bio_next_folio(struct folio_iter *fi, struct bio *bio)
 {
        fi->_seg_count -= fi->length;
        if (fi->_seg_count) {
-               fi->folio = folio_next(fi->folio);
+               fi->folio = __folio_next(fi->folio,
+                               (fi->offset + fi->length) / PAGE_SIZE);
                fi->offset = 0;
                fi->length = min(folio_size(fi->folio), fi->_seg_count);
        } else if (fi->_i + 1 < bio->bi_vcnt) {
diff --git a/include/linux/mm.h b/include/linux/mm.h
index de32c0383387..9c5547af8d0e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1642,6 +1642,12 @@ static inline long folio_nr_pages(struct folio *folio)
        return compound_nr(&folio->page);
 }

+static inline struct folio *__folio_next(struct folio *folio,
+               unsigned long nr_pages)
+{
+       return (struct folio *)folio_page(folio, nr_pages);
+}
+
 /**
  * folio_next - Move to the next physical folio.
  * @folio: The folio we're currently operating on.
@@ -1658,7 +1664,7 @@ static inline long folio_nr_pages(struct folio *folio)
  */
 static inline struct folio *folio_next(struct folio *folio)
 {
-       return (struct folio *)folio_page(folio, folio_nr_pages(folio));
+       return __folio_next(folio, folio_nr_pages(folio));
 }

 /**


Currently running Option A through its paces.