linux-kernel - Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for our internal use

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Message-ID: <c32642d6-6de2-eb2d-5771-c7cefa62fab5@kernel.org>
Date:   Mon, 5 Jul 2021 14:32:11 +0800
From:   Chao Yu <chao@...nel.org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [f2fs-dev] [PATCH] f2fs: initialize page->private when using for
 our internal use

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?

Cc Matthew Wilcox.

Thanks,

> 
> Fixes: b763f3bedc2d ("f2fs: restructure f2fs page.private layout")
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.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;
>