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Date:   Mon, 5 Jul 2021 01:56:59 -0700
From:   Jaegeuk Kim <jaegeuk@kernel.org>
To:     Chao Yu <chao@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-f2fs-devel@lists.sourceforge.net,
        Matthew Wilcox <willy@infradead.org>
Subject: Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for
 our internal use
Message-ID: <YOLJW0IgCagMk2tF@google.com>
References: <20210705052216.831989-1-jaegeuk@kernel.org>
 <c32642d6-6de2-eb2d-5771-c7cefa62fab5@kernel.org>
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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;
> >