[Ocfs2-devel] [PATCH] ocfs2: fstrim: Fix start offset of first cluster group during fstrim

[Junxiao Bi]

On 10/13/2017 03:12 AM, Ashish Samant wrote:
> The first cluster group descriptor is not stored at the start of the group
> but at an offset from the start. We need to take this into account while
> doing fstrim on the first cluster group. Otherwise we will wrongly start
> fstrim a few blocks after the desired start block and the range can cross
> over into the next cluster group and zero out the group descriptor there.
> This can cause filesytem corruption that cannot be fixed by fsck.
> 
> Signed-off-by: Ashish Samant <ashish.samant at oracle.com>
> Cc: stable at vger.kernel.org
Looks good.

Reviewed-by: Junxiao Bi <junxiao.bi at oracle.com>

> ---
>  fs/ocfs2/alloc.c | 24 ++++++++++++++++++------
>  1 file changed, 18 insertions(+), 6 deletions(-)
> 
> diff --git a/fs/ocfs2/alloc.c b/fs/ocfs2/alloc.c
> index a177eae..addd7c5 100644
> --- a/fs/ocfs2/alloc.c
> +++ b/fs/ocfs2/alloc.c
> @@ -7304,13 +7304,24 @@ int ocfs2_truncate_inline(struct inode *inode, struct buffer_head *di_bh,
>  
>  static int ocfs2_trim_extent(struct super_block *sb,
>  			     struct ocfs2_group_desc *gd,
> -			     u32 start, u32 count)
> +			     u64 group, u32 start, u32 count)
>  {
>  	u64 discard, bcount;
> +	struct ocfs2_super *osb = OCFS2_SB(sb);
>  
>  	bcount = ocfs2_clusters_to_blocks(sb, count);
> -	discard = le64_to_cpu(gd->bg_blkno) +
> -			ocfs2_clusters_to_blocks(sb, start);
> +	discard = ocfs2_clusters_to_blocks(sb, start);
> +
> +	/*
> +	 * For the first cluster group, the gd->bg_blkno is not at the start
> +	 * of the group, but at an offset from the start. If we add it while
> +	 * calculating discard for first group, we will wrongly start fstrim a
> +	 * few blocks after the desried start block and the range can cross
> +	 * over into the next cluster group. So, add it only if this is not
> +	 * the first cluster group.
> +	 */
> +	if (group != osb->first_cluster_group_blkno)
> +		discard += le64_to_cpu(gd->bg_blkno);
>  
>  	trace_ocfs2_trim_extent(sb, (unsigned long long)discard, bcount);
>  
> @@ -7318,7 +7329,7 @@ static int ocfs2_trim_extent(struct super_block *sb,
>  }
>  
>  static int ocfs2_trim_group(struct super_block *sb,
> -			    struct ocfs2_group_desc *gd,
> +			    struct ocfs2_group_desc *gd, u64 group,
>  			    u32 start, u32 max, u32 minbits)
>  {
>  	int ret = 0, count = 0, next;
> @@ -7337,7 +7348,7 @@ static int ocfs2_trim_group(struct super_block *sb,
>  		next = ocfs2_find_next_bit(bitmap, max, start);
>  
>  		if ((next - start) >= minbits) {
> -			ret = ocfs2_trim_extent(sb, gd,
> +			ret = ocfs2_trim_extent(sb, gd, group,
>  						start, next - start);
>  			if (ret < 0) {
>  				mlog_errno(ret);
> @@ -7435,7 +7446,8 @@ int ocfs2_trim_fs(struct super_block *sb, struct fstrim_range *range)
>  		}
>  
>  		gd = (struct ocfs2_group_desc *)gd_bh->b_data;
> -		cnt = ocfs2_trim_group(sb, gd, first_bit, last_bit, minlen);
> +		cnt = ocfs2_trim_group(sb, gd, group,
> +				       first_bit, last_bit, minlen);
>  		brelse(gd_bh);
>  		gd_bh = NULL;
>  		if (cnt < 0) {
>