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Message-ID: <ZDSaoHnlZbYMfbV7@google.com>
Date: Mon, 10 Apr 2023 16:24:16 -0700
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Chao Yu <chao@...nel.org>
Cc: Matthew Wilcox <willy@...radead.org>, linux-kernel@...r.kernel.org,
linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org,
linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [f2fs-dev] [PATCH] f2fs: get out of a repeat loop when getting a
locked data page
On 04/10, Chao Yu wrote:
> On 2023/4/6 11:18, Jaegeuk Kim wrote:
> > 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@...r.kernel.org>
> > > > > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.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:
> > > > 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 guess we are trying to maintain PagePrivate and page_private w/
> inner {set,clear}_page_private_* functions, if they are called in paired correctly,
> we don't need to call folio_detach_private() additionally in .release_folio and
> .invalid_folio, right? Otherwise there must be a bug.
Agreed.
>
> In this patch, I use bug_on to instead folio_detach_private().
> https://lore.kernel.org/linux-f2fs-devel/20230410022418.1843178-1-chao@kernel.org/
>
> In this patch, I use {attach,detach}_page_private() to clean up openned codes.
> https://lore.kernel.org/linux-f2fs-devel/20230410022418.1843178-2-chao@kernel.org/
Looks like it doesn't need to apply two patches, and missed f2fs_delete_entry
case as well.
>From 3fb0f570681dcd1c6c2f3e18ee7ff41428820b35 Mon Sep 17 00:00:00 2001
From: Chao Yu <chao@...nel.org>
Date: Mon, 10 Apr 2023 10:24:17 +0800
Subject: [PATCH] f2fs: remove folio_detach_private() in .invalidate_folio and
.release_folio
We have maintain PagePrivate and page_private and page reference
w/ {set,clear}_page_private_*, it doesn't need to call
folio_detach_private() in the end of .invalidate_folio and
.release_folio, remove it and use f2fs_bug_on instead.
Signed-off-by: Chao Yu <chao@...nel.org>
[Jaegeuk Kim: cover f2fs_delete_entry case]
Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
---
fs/f2fs/data.c | 4 ++--
fs/f2fs/dir.c | 5 ++---
fs/f2fs/f2fs.h | 32 ++++++++------------------------
3 files changed, 12 insertions(+), 29 deletions(-)
diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index 5a3636b70f48..8870ff630409 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -3734,7 +3734,7 @@ void f2fs_invalidate_folio(struct folio *folio, size_t offset, size_t length)
inode->i_ino == F2FS_COMPRESS_INO(sbi))
clear_page_private_data(&folio->page);
- folio_detach_private(folio);
+ f2fs_bug_on(sbi, page_private(&folio->page));
}
bool f2fs_release_folio(struct folio *folio, gfp_t wait)
@@ -3756,7 +3756,7 @@ bool f2fs_release_folio(struct folio *folio, gfp_t wait)
clear_page_private_reference(&folio->page);
clear_page_private_gcing(&folio->page);
- folio_detach_private(folio);
+ f2fs_bug_on(sbi, page_private(&folio->page));
return true;
}
diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
index d6dd8327e82d..cea179dec3b6 100644
--- a/fs/f2fs/dir.c
+++ b/fs/f2fs/dir.c
@@ -906,13 +906,12 @@ void f2fs_delete_entry(struct f2fs_dir_entry *dentry, struct page *page,
clear_page_dirty_for_io(page);
ClearPageUptodate(page);
+ clear_page_private_reference(page);
clear_page_private_gcing(page);
+ f2fs_bug_on(F2FS_I_SB(dir), page_private(page));
inode_dec_dirty_pages(dir);
f2fs_remove_dirty_inode(dir);
-
- detach_page_private(page);
- set_page_private(page, 0);
}
f2fs_put_page(page, 1);
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index 68eadc1ac130..1b1df9e33028 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -1408,11 +1408,8 @@ static inline bool page_private_##name(struct page *page) \
#define PAGE_PRIVATE_SET_FUNC(name, flagname) \
static inline void set_page_private_##name(struct page *page) \
{ \
- if (!PagePrivate(page)) { \
- get_page(page); \
- SetPagePrivate(page); \
- set_page_private(page, 0); \
- } \
+ if (!PagePrivate(page)) \
+ attach_page_private(page, (void *)0); \
set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)); \
set_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
}
@@ -1421,13 +1418,8 @@ static inline void set_page_private_##name(struct page *page) \
static inline void clear_page_private_##name(struct page *page) \
{ \
clear_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
- if (page_private(page) == BIT(PAGE_PRIVATE_NOT_POINTER)) { \
- set_page_private(page, 0); \
- if (PagePrivate(page)) { \
- ClearPagePrivate(page); \
- put_page(page); \
- }\
- } \
+ if (page_private(page) == BIT(PAGE_PRIVATE_NOT_POINTER)) \
+ detach_page_private(page); \
}
PAGE_PRIVATE_GET_FUNC(nonpointer, NOT_POINTER);
@@ -1456,11 +1448,8 @@ static inline unsigned long get_page_private_data(struct page *page)
static inline void set_page_private_data(struct page *page, unsigned long data)
{
- if (!PagePrivate(page)) {
- get_page(page);
- SetPagePrivate(page);
- set_page_private(page, 0);
- }
+ if (!PagePrivate(page))
+ attach_page_private(page, (void *)0);
set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page));
page_private(page) |= data << PAGE_PRIVATE_MAX;
}
@@ -1468,13 +1457,8 @@ static inline void set_page_private_data(struct page *page, unsigned long data)
static inline void clear_page_private_data(struct page *page)
{
page_private(page) &= GENMASK(PAGE_PRIVATE_MAX - 1, 0);
- if (page_private(page) == BIT(PAGE_PRIVATE_NOT_POINTER)) {
- set_page_private(page, 0);
- if (PagePrivate(page)) {
- ClearPagePrivate(page);
- put_page(page);
- }
- }
+ if (page_private(page) == BIT(PAGE_PRIVATE_NOT_POINTER))
+ detach_page_private(page);
}
/* For compression */
--
2.40.0.577.gac1e443424-goog
>
> With above two patches, I didn't hit any panic or use-after-free issue when testing
> xfstest until now.
>
> Thanks,
>
>
> > 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);
> > > > > > > > }
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