Re: [PATCH v2 1/3] ext4: add two helper functions extent_logical_end() and pa_logical_end()

[Ritesh Harjani (IBM) <ritesh.list@gmail.com>]

Baokun Li <libaokun1@huawei.com> writes:

> When we use lstart + len to calculate the end of free extent or prealloc
> space, it may exceed the maximum value of 4294967295(0xffffffff) supported
> by ext4_lblk_t and cause overflow, which may lead to various problems.
>
> Therefore, we add two helper functions, extent_logical_end() and
> pa_logical_end(), to limit the type of end to loff_t, and also convert
> lstart to loff_t for calculation to avoid overflow.

Sure. extent_logical_end() is not as bad after dropping the third param.
Thanks for addressing review comments and identifying overflow issues :) 

Looks good to me. Feel free to add: 

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


>
> Signed-off-by: Baokun Li <libaokun1@huawei.com>
> ---
>  fs/ext4/mballoc.c |  9 +++------
>  fs/ext4/mballoc.h | 14 ++++++++++++++
>  2 files changed, 17 insertions(+), 6 deletions(-)
>
> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
> index 21b903fe546e..4cb13b3e41b3 100644
> --- a/fs/ext4/mballoc.c
> +++ b/fs/ext4/mballoc.c
> @@ -4432,7 +4432,7 @@ ext4_mb_normalize_request(struct ext4_allocation_context *ac,
>  
>  	/* first, let's learn actual file size
>  	 * given current request is allocated */
> -	size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
> +	size = extent_logical_end(sbi, &ac->ac_o_ex);
>  	size = size << bsbits;
>  	if (size < i_size_read(ac->ac_inode))
>  		size = i_size_read(ac->ac_inode);
> @@ -4766,7 +4766,6 @@ ext4_mb_use_preallocated(struct ext4_allocation_context *ac)
>  	struct ext4_inode_info *ei = EXT4_I(ac->ac_inode);
>  	struct ext4_locality_group *lg;
>  	struct ext4_prealloc_space *tmp_pa = NULL, *cpa = NULL;
> -	loff_t tmp_pa_end;
>  	struct rb_node *iter;
>  	ext4_fsblk_t goal_block;
>  
> @@ -4862,9 +4861,7 @@ ext4_mb_use_preallocated(struct ext4_allocation_context *ac)
>  	 * pa can possibly satisfy the request hence check if it overlaps
>  	 * original logical start and stop searching if it doesn't.
>  	 */
> -	tmp_pa_end = (loff_t)tmp_pa->pa_lstart + EXT4_C2B(sbi, tmp_pa->pa_len);
> -
> -	if (ac->ac_o_ex.fe_logical >= tmp_pa_end) {
> +	if (ac->ac_o_ex.fe_logical >= pa_logical_end(sbi, tmp_pa)) {
>  		spin_unlock(&tmp_pa->pa_lock);
>  		goto try_group_pa;
>  	}
> @@ -5769,7 +5766,7 @@ static void ext4_mb_group_or_file(struct ext4_allocation_context *ac)
>  
>  	group_pa_eligible = sbi->s_mb_group_prealloc > 0;
>  	inode_pa_eligible = true;
> -	size = ac->ac_o_ex.fe_logical + EXT4_C2B(sbi, ac->ac_o_ex.fe_len);
> +	size = extent_logical_end(sbi, &ac->ac_o_ex);
>  	isize = (i_size_read(ac->ac_inode) + ac->ac_sb->s_blocksize - 1)
>  		>> bsbits;
>  
> diff --git a/fs/ext4/mballoc.h b/fs/ext4/mballoc.h
> index df6b5e7c2274..d7aeb5da7d86 100644
> --- a/fs/ext4/mballoc.h
> +++ b/fs/ext4/mballoc.h
> @@ -233,6 +233,20 @@ static inline ext4_fsblk_t ext4_grp_offs_to_block(struct super_block *sb,
>  		(fex->fe_start << EXT4_SB(sb)->s_cluster_bits);
>  }
>  
> +static inline loff_t extent_logical_end(struct ext4_sb_info *sbi,
> +					struct ext4_free_extent *fex)
> +{
> +	/* Use loff_t to avoid end exceeding ext4_lblk_t max. */
> +	return (loff_t)fex->fe_logical + EXT4_C2B(sbi, fex->fe_len);
> +}
> +
> +static inline loff_t pa_logical_end(struct ext4_sb_info *sbi,
> +				    struct ext4_prealloc_space *pa)
> +{
> +	/* Use loff_t to avoid end exceeding ext4_lblk_t max. */
> +	return (loff_t)pa->pa_lstart + EXT4_C2B(sbi, pa->pa_len);
> +}
> +
>  typedef int (*ext4_mballoc_query_range_fn)(
>  	struct super_block		*sb,
>  	ext4_group_t			agno,
> -- 
> 2.31.1