Re: [f2fs-dev] [PATCH] f2fs: get out of a repeat loop when getting a locked data page

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On 2023/3/27 23:30, Jaegeuk Kim wrote:
On 03/26, Chao Yu wrote:
On 2023/3/24 5:39, Jaegeuk Kim wrote:

Somehow we're getting a page which has a different mapping.
Let's avoid the infinite loop.

Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx>
   fs/f2fs/data.c | 8 ++------
   1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index bf51e6e4eb64..80702c93e885 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1329,18 +1329,14 @@ struct page *f2fs_get_lock_data_page(struct inode *inode, pgoff_t index,
   	struct address_space *mapping = inode->i_mapping;
   	struct page *page;
   	page = f2fs_get_read_data_page(inode, index, 0, for_write, NULL);
   	if (IS_ERR(page))
   		return page;
   	/* wait for read completion */
-	if (unlikely(page->mapping != mapping)) {

How about using such logic only for move_data_page() to limit affect for
other paths?

Why move_data_page() only? If this happens, we'll fall into a loop in anywhere?

Actually, we only suffer dead loop from foreground GC path, right? I suspect the
bug was triggered in this path only.

It looks there are a lot of cases in where we repeat triggering read once
two mappings are mismatched, e.g.
- __get_meta_page
- __get_node_page
- f2fs_write_begin
- f2fs_quota_read


Jaegeuk, any thoughts about why mapping is mismatch in between page's one and

After several times code review, I didn't get any clue about why f2fs always
get the different mapping in a loop.

I couldn't find the path to happen this. So weird. Please check the history in the

Maybe we can loop MM guys to check whether below folio_file_page() may return
page which has different mapping?

Matthew may have some idea on this?

struct page *pagecache_get_page(struct address_space *mapping, pgoff_t index,
		int fgp_flags, gfp_t gfp)
	struct folio *folio;

	folio = __filemap_get_folio(mapping, index, fgp_flags, gfp);
	if (IS_ERR(folio))
		return NULL;
	return folio_file_page(folio, index);


-		f2fs_put_page(page, 1);
-		goto repeat;
-	}
-	if (unlikely(!PageUptodate(page))) {
+	if (unlikely(page->mapping != mapping || !PageUptodate(page))) {
   		f2fs_put_page(page, 1);
   		return ERR_PTR(-EIO);

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