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Two folio fixes for 5.18:

Browse source 
- Fix a race when we were calling folio_next() in the BIO folio iter
    without holding a reference, meaning the folio could be split or freed,
    and we'd jump to the next page instead of the intended next folio.
 
  - Fix readahead creating single-page folios instead of the intended
    large folios when doing reads that are not a power of two in size.
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Merge tag 'folio-5.18f' of git://git.infradead.org/users/willy/pagecache

Pull folio fixes from Matthew Wilcox:
 "Two folio fixes for 5.18.

  Darrick and Brian have done amazing work debugging the race I created
  in the folio BIO iterator. The readahead problem was deterministic, so
  easy to fix.

   - Fix a race when we were calling folio_next() in the BIO folio iter
     without holding a reference, meaning the folio could be split or
     freed, and we'd jump to the next page instead of the intended next
     folio.

   - Fix readahead creating single-page folios instead of the intended
     large folios when doing reads that are not a power of two in size"

* tag 'folio-5.18f' of git://git.infradead.org/users/willy/pagecache:
  mm/readahead: Fix readahead with large folios
  block: Do not call folio_next() on an unreferenced folio
This commit is contained in:
Linus Torvalds 2022-05-05 16:52:15 -07:00
commit fe27d189e3
2 changed files with 13 additions and 7 deletions
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5
include/linux/bio.h
View file

@ -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;
};
@ -283,6 +284,7 @@ static inline void bio_first_folio(struct folio_iter *fi, struct bio *bio,
PAGE_SIZE * (bvec->bv_page - &fi->folio->page);
fi->_seg_count = bvec->bv_len;
fi->length = min(folio_size(fi->folio) - fi->offset, fi->_seg_count);
fi->_next = folio_next(fi->folio);
fi->_i = i;
}
@ -290,9 +292,10 @@ 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);
fi->_next = folio_next(fi->folio);
} else if (fi->_i + 1 < bio->bi_vcnt) {
bio_first_folio(fi, bio, fi->_i + 1);
} else {