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@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
Looks good.
Reviewed-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
> ---
> 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) {
>