linux-kernel - Re: [f2fs-dev] [PATCH 1/3] f2fs: call flush_dcache

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Date:	Thu, 20 Nov 2014 17:47:29 +0900
From:	Changman Lee <cm224.lee@...sung.com>
To:	Jaegeuk Kim <jaegeuk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	linux-f2fs-devel@...ts.sourceforge.net
Subject: Re: [f2fs-dev] [PATCH 1/3] f2fs: call flush_dcache_page when the page
 was updated

On Wed, Nov 19, 2014 at 10:45:33PM -0800, Jaegeuk Kim wrote:
> On Thu, Nov 20, 2014 at 03:04:10PM +0900, Changman Lee wrote:
> > Hi Jaegeuk,
> > 
> > We should call flush_dcache_page before kunmap because the purpose of the cache flush is to address aliasing problem related to virtual address.
> 
> Oh, I just followed zero_user_segments below.
> 
> static inline void zero_user_segments(struct page *page,
> 	unsigned start1, unsigned end1,
> 	unsigned start2, unsigned end2)
> {
> 	void *kaddr = kmap_atomic(page);
> 
> 	BUG_ON(end1 > PAGE_SIZE || end2 > PAGE_SIZE);
> 
> 	if (end1 > start1)
> 		memset(kaddr + start1, 0, end1 - start1);
> 
> 	if (end2 > start2)
> 		memset(kaddr + start2, 0, end2 - start2);
> 
> 	kunmap_atomic(kaddr);
> 	flush_dcache_page(page);
> }
> 
> Is this a wrong reference? Or, a bug?
> 

Well.. Data in cache only have to be flushed until before other users read the data.
If so, it's not a bug.

> Anyway I modified as below.
> 
> Thanks,
> 
> >From 7cb7b27c8cd2efc8a31d79239bef5b41c6e79216 Mon Sep 17 00:00:00 2001
> From: Jaegeuk Kim <jaegeuk@...nel.org>
> Date: Tue, 18 Nov 2014 10:50:21 -0800
> Subject: [PATCH] f2fs: call flush_dcache_page when the page was updated
> 
> Whenever f2fs updates mapped pages, it needs to call flush_dcache_page.
> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/dir.c    | 7 ++++++-
>  fs/f2fs/inline.c | 2 ++
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index 5a49995..fabf4ee 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -287,8 +287,10 @@ void f2fs_set_link(struct inode *dir, struct f2fs_dir_entry *de,
>  	f2fs_wait_on_page_writeback(page, type);
>  	de->ino = cpu_to_le32(inode->i_ino);
>  	set_de_type(de, inode);
> -	if (!f2fs_has_inline_dentry(dir))
> +	if (!f2fs_has_inline_dentry(dir)) {
> +		flush_dcache_page(page);
>  		kunmap(page);
> +	}
>  	set_page_dirty(page);
>  	dir->i_mtime = dir->i_ctime = CURRENT_TIME;
>  	mark_inode_dirty(dir);
> @@ -365,6 +367,7 @@ static int make_empty_dir(struct inode *inode,
>  	make_dentry_ptr(&d, (void *)dentry_blk, 1);
>  	do_make_empty_dir(inode, parent, &d);
>  
> +	flush_dcache_page(dentry_page);
>  	kunmap_atomic(dentry_blk);
>  
>  	set_page_dirty(dentry_page);
> @@ -578,6 +581,7 @@ fail:
>  		update_inode_page(dir);
>  		clear_inode_flag(F2FS_I(dir), FI_UPDATE_DIR);
>  	}
> +	flush_dcache_page(dentry_page);
>  	kunmap(dentry_page);
>  	f2fs_put_page(dentry_page, 1);
>  	return err;
> @@ -660,6 +664,7 @@ void f2fs_delete_entry(struct f2fs_dir_entry *dentry, struct page *page,
>  	bit_pos = find_next_bit_le(&dentry_blk->dentry_bitmap,
>  			NR_DENTRY_IN_BLOCK,
>  			0);
> +	flush_dcache_page(page);
>  	kunmap(page); /* kunmap - pair of f2fs_find_entry */
>  	set_page_dirty(page);
>  
> diff --git a/fs/f2fs/inline.c b/fs/f2fs/inline.c
> index f26fb87..4291c1f 100644
> --- a/fs/f2fs/inline.c
> +++ b/fs/f2fs/inline.c
> @@ -106,6 +106,7 @@ int f2fs_convert_inline_page(struct dnode_of_data *dn, struct page *page)
>  	src_addr = inline_data_addr(dn->inode_page);
>  	dst_addr = kmap_atomic(page);
>  	memcpy(dst_addr, src_addr, MAX_INLINE_DATA);
> +	flush_dcache_page(page);
>  	kunmap_atomic(dst_addr);
>  	SetPageUptodate(page);
>  no_update:
> @@ -357,6 +358,7 @@ static int f2fs_convert_inline_dir(struct inode *dir, struct page *ipage,
>  	memcpy(dentry_blk->filename, inline_dentry->filename,
>  					NR_INLINE_DENTRY * F2FS_SLOT_LEN);
>  
> +	flush_dcache_page(page);
>  	kunmap_atomic(dentry_blk);
>  	SetPageUptodate(page);
>  	set_page_dirty(page);
> -- 
> 2.1.1
> 
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