Re: [RFC v3 4/8] ext4: Move overlap assert logic into a separate function

Jan Kara
2022-09-29T11:32:07Z

On Tue 27-09-22 14:46:44, Ojaswin Mujoo wrote:
> Abstract out the logic to double check for overlaps in normalize_pa to
> a separate function. Since there has been no reports in past where we
> have seen any overlaps which hits this bug_on(), in future we can
> consider calling this function under "#ifdef AGGRESSIVE_CHECK" only.
>
> There are no functional changes in this patch
>
> Signed-off-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@suse.cz>

And I agree it might be interesting to move this code under appropriate
ifdef.

Honza

> ---
> fs/ext4/mballoc.c | 36 ++++++++++++++++++++++++------------
> 1 file changed, 24 insertions(+), 12 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 84950df709bb..d1ce34888dcc 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -3985,6 +3985,29 @@ static void ext4_mb_normalize_group_request(struct ext4_allocation_context *ac)
> mb_debug(sb, "goal %u blocks for locality group\n", ac->ac_g_ex.fe_len);
> }
>
> +static inline void
> +ext4_mb_pa_assert_overlap(struct ext4_allocation_context *ac,
> + ext4_lblk_t start, ext4_lblk_t end)
> +{
> + struct ext4_sb_info *sbi = EXT4_SB(ac->ac_sb);
> + struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
> + struct ext4_prealloc_space *tmp_pa;
> + ext4_lblk_t tmp_pa_start, tmp_pa_end;
> +
> + rcu_read_lock();
> + list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
> + spin_lock(&tmp_pa->pa_lock);
> + if (tmp_pa->pa_deleted == 0) {
> + tmp_pa_start = tmp_pa->pa_lstart;
> + tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> +
> + BUG_ON(!(start >= tmp_pa_end || end <= tmp_pa_start));
> + }
> + spin_unlock(&tmp_pa->pa_lock);
> + }
> + rcu_read_unlock();
> +}
> +
> /*
> * Normalization means making request better in terms of
> * size and alignment
> @@ -4141,18 +4164,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
> size = end - start;
>
> /* XXX: extra loop to check we really don't overlap preallocations */
> - rcu_read_lock();
> - list_for_each_entry_rcu(tmp_pa, &ei->i_prealloc_list, pa_inode_list) {
> - spin_lock(&tmp_pa->pa_lock);
> - if (tmp_pa->pa_deleted == 0) {
> - tmp_pa_start = tmp_pa->pa_lstart;
> - tmp_pa_end = tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> -
> - BUG_ON(!(start >= tmp_pa_end || end <= tmp_pa_start));
> - }
> - spin_unlock(&tmp_pa->pa_lock);
> - }
> - rcu_read_unlock();
> + ext4_mb_pa_assert_overlap(ac, start, end);
>
> /*
> * In this function "start" and "size" are normalized for better
> --
> 2.31.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR