linux-kernel - RE: [f2fs-dev] [PATCH 3/3] f2fs: allow zeroed name length during find

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Message-id: <018b01d0bfae$ce294410$6a7bcc30$@samsung.com>
Date:	Thu, 16 Jul 2015 18:03:46 +0800
From:	Chao Yu <chao2.yu@...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 3/3] f2fs: allow zeroed name length during
	find_dentry

Hi Jaegeuk,

> -----Original Message-----
> From: Jaegeuk Kim [mailto:jaegeuk@...nel.org]
> Sent: Thursday, July 16, 2015 6:38 AM
> To: linux-kernel@...r.kernel.org; linux-fsdevel@...r.kernel.org;
> linux-f2fs-devel@...ts.sourceforge.net
> Cc: Jaegeuk Kim
> Subject: [f2fs-dev] [PATCH 3/3] f2fs: allow zeroed name length during find_dentry
> 
> Since find_dentry doesn't lock its dentry page, it can traverse intermediate
> bit positions consisting of a big dentry.
> For these bit positions, this patch fills the intermediate name length fields
> as zeros and skips them during look-up.

I didn't get it, AFAIK, dentry page will be accessed under protection of
i_mutex, if our inode operation has no bug, why this zeroed name_len can
exist?

Thanks,

> 
> Signed-off-by: Jaegeuk Kim <jaegeuk@...nel.org>
> ---
>  fs/f2fs/dir.c | 20 ++++++++++++++------
>  1 file changed, 14 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/f2fs/dir.c b/fs/f2fs/dir.c
> index a34ebd8..71195f5 100644
> --- a/fs/f2fs/dir.c
> +++ b/fs/f2fs/dir.c
> @@ -141,11 +141,15 @@ struct f2fs_dir_entry *find_target_dentry(struct f2fs_filename *fname,
>  			*max_slots = max_len;
>  		max_len = 0;
> 
> -		/* remain bug on condition */
> -		if (unlikely(!de->name_len))
> -			d->max = -1;
> -
> -		bit_pos += GET_DENTRY_SLOTS(le16_to_cpu(de->name_len));
> +		/*
> +		 * While a large dentry is adding, it can traverse its valid bit
> +		 * positions, since find_entry does not lock its dentry page.
> +		 * In that case, let's skip the bit position.
> +		 */
> +		if (de_name.len == 0)
> +			bit_pos++;
> +		else
> +			bit_pos += GET_DENTRY_SLOTS(de_name.len);
>  	}
> 
>  	de = NULL;
> @@ -505,8 +509,12 @@ void f2fs_update_dentry(nid_t ino, umode_t mode, struct f2fs_dentry_ptr
> *d,
>  	memcpy(d->filename[bit_pos], name->name, name->len);
>  	de->ino = cpu_to_le32(ino);
>  	set_de_type(de, mode);
> -	for (i = 0; i < slots; i++)
> +	for (i = 0; i < slots; i++) {
> +		/* fill zeros for intermediate name_len slots */
> +		if (i >= 1)
> +			d->dentry[bit_pos + i].name_len = 0;
>  		test_and_set_bit_le(bit_pos + i, (void *)d->bitmap);
> +	}
>  }
> 
>  /*
> --
> 2.1.1
> 
> 
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