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

[Baokun Li]

On 2023/7/26 1:29, Ritesh Harjani (IBM) wrote:
> Baokun Li <libaokun1@xxxxxxxxxx> 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@xxxxxxxxx>
Thank you very much for your patient review! 😊
> > Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> > ---
> >   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
Cheers!
--
With Best Regards,
Baokun Li
.