Before this commit[1], we used to call iomap_page_create() before checking folio_test_uptodate() in __iomap_write_begin(). The problem is that commit[1] moved iop creation later i.e. after checking for whether the folio is uptodate. And if the folio is uptodate, it simply returns and doesn't allocate a iop. Now what can happen is that during __iomap_write_begin() for bs < ps, there can be a folio which is marked uptodate but does not have a iomap_page structure allocated. (I think one of the reason it can happen is due to memory pressure, we can end up freeing folio->private resource). Thus the iop structure will only gets allocated at the time of writeback in iomap_writepage_map(). This I think, was a not problem till now since we anyway only track uptodate status in iop (no support of tracking dirty bitmap status which later patches will add), and we also end up setting all the bits in iomap_page_create(), if the page is uptodate. [1]: https://lore.kernel.org/all/20220623175157.1715274-5-shr@xxxxxx/ Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@xxxxxxxxx> --- fs/iomap/buffered-io.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c index 356193e44cf0..e9c85fcf7a1f 100644 --- a/fs/iomap/buffered-io.c +++ b/fs/iomap/buffered-io.c @@ -527,7 +527,8 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos, size_t len, struct folio *folio) { const struct iomap *srcmap = iomap_iter_srcmap(iter); - struct iomap_page *iop; + struct iomap_page *iop = iomap_page_create(iter->inode, folio, + iter->flags); loff_t block_size = i_blocksize(iter->inode); loff_t block_start = round_down(pos, block_size); loff_t block_end = round_up(pos + len, block_size); @@ -539,7 +540,6 @@ static int __iomap_write_begin(const struct iomap_iter *iter, loff_t pos, return 0; folio_clear_error(folio); - iop = iomap_page_create(iter->inode, folio, iter->flags); if ((iter->flags & IOMAP_NOWAIT) && !iop && nr_blocks > 1) return -EAGAIN; -- 2.39.1
