Re: generic/068 crash on 5.18-rc2?

Matthew Wilcox
2022-04-30T21:40:41Z

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.