[PATCH v2] iomap: Move page_done callback under the folio lock

Andreas Gruenbacher
2022-12-14T10:25:14Z

Move the ->page_done() call in iomap_write_end() under the folio lock.
This closes a race between journaled data writes and the shrinker in
gfs2. What's happening is that gfs2_iomap_page_done() is called after
the page has been unlocked, so try_to_free_buffers() can come in and
free the buffers while gfs2_iomap_page_done() is trying to add them to
the current transaction. The folio lock prevents that from happening.

The only current user of ->page_done() is gfs2, so other filesystems are
not affected. Still, to catch out any new users, switch from page to
folio in ->page_done().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
fs/gfs2/bmap.c | 7 ++++---
fs/iomap/buffered-io.c | 4 ++--
include/linux/iomap.h | 10 +++++-----
3 files changed, 11 insertions(+), 10 deletions(-)

diff --git a/fs/gfs2/bmap.c b/fs/gfs2/bmap.c
index e7537fd305dd..c4ee47f8e499 100644
--- a/fs/gfs2/bmap.c
+++ b/fs/gfs2/bmap.c
@@ -968,14 +968,15 @@ static int gfs2_iomap_page_prepare(struct inode *inode, loff_t pos,
}

static void gfs2_iomap_page_done(struct inode *inode, loff_t pos,
- unsigned copied, struct page *page)
+ unsigned copied, struct folio *folio)
{
struct gfs2_trans *tr = current->journal_info;
struct gfs2_inode *ip = GFS2_I(inode);
struct gfs2_sbd *sdp = GFS2_SB(inode);

- if (page && !gfs2_is_stuffed(ip))
- gfs2_page_add_databufs(ip, page, offset_in_page(pos), copied);
+ if (folio && !gfs2_is_stuffed(ip))
+ gfs2_page_add_databufs(ip, &folio->page, offset_in_page(pos),
+ copied);

if (tr->tr_num_buf_new)
__mark_inode_dirty(inode, I_DIRTY_DATASYNC);
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 91ee0b308e13..d988c1bedf70 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -714,12 +714,12 @@ static size_t iomap_write_end(struct iomap_iter *iter, loff_t pos, size_t len,
i_size_write(iter->inode, pos + ret);
iter->iomap.flags |= IOMAP_F_SIZE_CHANGED;
}
+ if (page_ops && page_ops->page_done)
+ page_ops->page_done(iter->inode, pos, ret, folio);
folio_unlock(folio);

if (old_size < pos)
pagecache_isize_extended(iter->inode, old_size, pos);
- if (page_ops && page_ops->page_done)
- page_ops->page_done(iter->inode, pos, ret, &folio->page);
folio_put(folio);

if (ret < len)
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 238a03087e17..bd6d80453726 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -116,18 +116,18 @@ static inline bool iomap_inline_data_valid(const struct iomap *iomap)

/*
* When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
- * and page_done will be called for each page written to. This only applies to
- * buffered writes as unbuffered writes will not typically have pages
+ * and page_done will be called for each folio written to. This only applies
+ * to buffered writes as unbuffered writes will not typically have folios
* associated with them.
*
* When page_prepare succeeds, page_done will always be called to do any
- * cleanup work necessary. In that page_done call, @page will be NULL if the
- * associated page could not be obtained.
+ * cleanup work necessary. In that page_done call, @folio will be NULL if the
+ * associated folio could not be obtained.
*/
struct iomap_page_ops {
int (*page_prepare)(struct inode *inode, loff_t pos, unsigned len);
void (*page_done)(struct inode *inode, loff_t pos, unsigned copied,
- struct page *page);
+ struct folio *folio);
};

/*
--
2.38.1