On 2023/4/6 0:39, Jaegeuk Kim wrote:
On 03/27, Matthew Wilcox wrote:
On Mon, Mar 27, 2023 at 08:30:33AM -0700, Jaegeuk Kim wrote:
On 03/26, Chao Yu wrote:
On 2023/3/24 5:39, Jaegeuk Kim wrote:
https://bugzilla.kernel.org/show_bug.cgi?id=216050
Somehow we're getting a page which has a different mapping. Let's avoid the infinite loop.
Cc: stable@vger.kernel.org Signed-off-by: Jaegeuk Kim jaegeuk@kernel.org
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; -repeat:
- page = f2fs_get_read_data_page(inode, index, 0, for_write, NULL); if (IS_ERR(page)) return page; /* wait for read completion */ lock_page(page);
- 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?
Jaegeuk, any thoughts about why mapping is mismatch in between page's one and inode->i_mapping?
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 bug.
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?
There's a lot of comments in the bug ... hard to come into this one cold.
I did notice this one (#119): : Interestingly, ref count is 514, which looks suspiciously as a binary : flag 1000000010. Is it possible that during 5.17/5.18 implementation : of a "pin", somehow binary flag was written to ref count, or something : like '1 << ...' happens?
That indicates to me that somehow you've got hold of a THP that is in the page cache. Probably shmem/tmpfs. That indicate to me a refcount problem that looks something like this:
f2fs allocates a page f2fs adds the page to the page cache f2fs puts the reference to the page without removing it from the page cache (how?)
Is it somewhat related to setting a bit in private field?
IIUC, it looks the page reference is added/removed as pair.
When we migrate the blocks, we do:
- get_lock_page()
- f2fs_grab_cache_page - pagecache_get_page - __filemap_get_folio - no_page -> filemap_alloc_folio page_ref = 1 (referenced by caller) - filemap_add_folio page_ref = 2 (referenced by radix tree)
- submit read
- lock_page()
- set_page_dirty()
- set_page_private_gcing(page)
page_ref = 3 (reference by private data)
--- in fs/f2fs/f2fs.h 1409 #define PAGE_PRIVATE_SET_FUNC(name, flagname) \ 1410 static inline void set_page_private_##name(struct page *page) \ 1411 { \ 1412 if (!PagePrivate(page)) { \ 1413 get_page(page); \ 1414 SetPagePrivate(page); \ 1415 set_page_private(page, 0); \ 1416 } \ 1417 set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)); \ 1418 set_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \ 1419 }
- set_page_writebac()
- submit write
- unlock_page()
- put_page(page)
page_ref = 2 (ref by caller was removed)
Later, f2fs_invalidate_folio will do put_page again by: clear_page_private_gcing(&folio->page);
page_ref = 1 (ref by private was removed, and the last left ref is hold by radix tree)
--- in fs/f2fs/f2fs.h 1421 #define PAGE_PRIVATE_CLEAR_FUNC(name, flagname) \ 1422 static inline void clear_page_private_##name(struct page *page) \ 1423 { \ 1424 clear_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \ 1425 if (page_private(page) == BIT(PAGE_PRIVATE_NOT_POINTER)) { \ 1426 set_page_private(page, 0); \ 1427 if (PagePrivate(page)) { \ 1428 ClearPagePrivate(page); \
Since PagePrivate was cleared, so folio_detach_private in f2fs_invalidate_folio()/f2fs_release_folio will just skip drop reference.
static inline void *folio_detach_private(struct folio *folio) { void *data = folio_get_private(folio);
if (!folio_test_private(folio)) return NULL; folio_clear_private(folio); folio->private = NULL; folio_put(folio);
return data; }
Or am I missing something?
Thanks,
1429 put_page(page); \ 1430 }\ 1431 } \ 1432 }
page is now free, gets reallocated into a THP lookup from the f2fs file finds the new THP things explode messily
Checking page->mapping is going to avoid the messy explosion, but you'll still have a page in the page cache which doesn't actually belong to you, and that's going to lead to subtle data corruption.
This should be caught by page_expected_state(), called from free_page_is_bad(), called from free_pages_prepare(). Do your testers have CONFIG_DEBUG_VM enabled? That might give you a fighting chance at finding the last place which called put_page(). It won't necessarily be the _wrong_ place to call put_page() (that may have happened earlier), but it may give you a clue.
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); }
Thanks,
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); }