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SubjectRe: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for our internal use
On 07/05, Chao Yu wrote:
> On 2021/7/5 13:22, Jaegeuk Kim wrote:
> > We need to guarantee it's initially zero. Otherwise, it'll hurt entire flag
> > operations.
>
> Oops, I didn't get the point, shouldn't .private be zero after page was
> just allocated by filesystem? What's the case we will encounter stall
> private data left in page?

I'm seeing f2fs_migrate_page() has the newpage with some value without Private
flag. That causes a kernel panic later due to wrong private flag used in f2fs.

>
> Cc Matthew Wilcox.
>
> Thanks,
>
> >
> > Fixes: b763f3bedc2d ("f2fs: restructure f2fs page.private layout")
> > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
> > ---
> > fs/f2fs/data.c | 2 ++
> > fs/f2fs/f2fs.h | 5 ++++-
> > 2 files changed, 6 insertions(+), 1 deletion(-)
> >
> > diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
> > index 3a01a1b50104..d2cf48c5a2e4 100644
> > --- a/fs/f2fs/data.c
> > +++ b/fs/f2fs/data.c
> > @@ -3819,6 +3819,8 @@ int f2fs_migrate_page(struct address_space *mapping,
> > get_page(newpage);
> > }
> > + /* guarantee to start from no stale private field */
> > + set_page_private(newpage, 0);
> > if (PagePrivate(page)) {
> > set_page_private(newpage, page_private(page));
> > SetPagePrivate(newpage);
> > diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
> > index 65befc68d88e..ee8eb33e2c25 100644
> > --- a/fs/f2fs/f2fs.h
> > +++ b/fs/f2fs/f2fs.h
> > @@ -1331,7 +1331,8 @@ enum {
> > #define PAGE_PRIVATE_GET_FUNC(name, flagname) \
> > static inline bool page_private_##name(struct page *page) \
> > { \
> > - return test_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)) && \
> > + return PagePrivate(page) && \
> > + test_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)) && \
> > test_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
> > }
> > @@ -1341,6 +1342,7 @@ static inline void set_page_private_##name(struct page *page) \
> > if (!PagePrivate(page)) { \
> > get_page(page); \
> > SetPagePrivate(page); \
> > + set_page_private(page, 0); \
> > } \
> > set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page)); \
> > set_bit(PAGE_PRIVATE_##flagname, &page_private(page)); \
> > @@ -1392,6 +1394,7 @@ 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);
> > }
> > set_bit(PAGE_PRIVATE_NOT_POINTER, &page_private(page));
> > page_private(page) |= data << PAGE_PRIVATE_MAX;
> >

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