On 04/06, Chao Yu wrote: > 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@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; > > > > > > -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: > > 1) 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) > > > 2) submit read > > 3) lock_page() > > 3) set_page_dirty() > > 4) 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 } > > > > > > 5) set_page_writebac() > > 6) submit write > > 7) unlock_page() > > 8) 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? Ah, I missed folio_test_private() tho, can we really expect get_page(), SetPagePrivate(), and set_page_private() is in pair with folio_detach_private()? I feel attach/detach_page_private would look better? > > 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); > > > > > > }
