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

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Date:   Thu, 29 Sep 2022 13:32:01 +0200
From:   Jan Kara <jack@...e.cz>
To:     Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc:     linux-ext4@...r.kernel.org, Theodore Ts'o <tytso@....edu>,
        Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, rookxu <brookxu.cn@...il.com>,
        Ritesh Harjani <ritesh.list@...il.com>
Subject: Re: [RFC v3 4/8] ext4: Move overlap assert logic into a separate
 function

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@...ux.ibm.com>
> Reviewed-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>

Looks good. Feel free to add:

Reviewed-by: Jan Kara <jack@...e.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@...e.com>
SUSE Labs, CR