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Message-ID: <b83ddb0e-0411-1ca8-dd76-238db056b710@kernel.org> Date: Mon, 5 Jun 2023 12:15:32 +0800 From: Chao Yu <chao@...nel.org> To: Theodore Ts'o <tytso@....edu> Cc: Andreas Dilger <adilger.kernel@...ger.ca>, linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org, Jan Kara <jack@...e.cz> Subject: Re: [PATCH] ext4: fix wrong calculation of minlen in ext4_trim_fs() Ping, On 2023/4/21 17:35, Jan Kara wrote: > On Thu 06-04-23 23:06:21, Chao Yu wrote: >> As Ted pointed out as below: >> >> " >> However the minlen variable in ext4_trim_fs is in units of *clusters*. >> And so it gets rounded up two places. The first time is when it is >> converted into units of a cluster: >> >> minlen = EXT4_NUM_B2C(EXT4_SB(sb), >> range->minlen >> sb->s_blocksize_bits); >> >> Oh, and by the way, that first conversion is not correct as currently >> written in ext4_fs_trim(). It should be >> >> minlen = (range->minlen + EXT4_CLUSTER_SIZE(sb) - 1) >> >> (sb->s_blocksize_bits + EXT4_CLUSTER_BITS(sb)); >> " >> >> The reason is if range->minlen is smaller than block size of ext4, >> original calculation "range->minlen >> sb->s_blocksize_bits" may >> return zero, but since EXT4_NUM_B2C() expects a non-zero in-parameter, >> so it needs to round up range->minlen to cluster size directly as above. >> >> Link: https://lore.kernel.org/lkml/20230311031843.GF860405@mit.edu/ >> Suggested-by: Theodore Ts'o <tytso@....edu> >> Signed-off-by: Chao Yu <chao@...nel.org> > > Looks good to me. Feel free to add: > > Reviewed-by: Jan Kara <jack@...e.cz> > > Honza > >> --- >> fs/ext4/mballoc.c | 4 ++-- >> 1 file changed, 2 insertions(+), 2 deletions(-) >> >> diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c >> index 5b2ae37a8b80..d8b9d6a83d1e 100644 >> --- a/fs/ext4/mballoc.c >> +++ b/fs/ext4/mballoc.c >> @@ -6478,8 +6478,8 @@ int ext4_trim_fs(struct super_block *sb, struct fstrim_range *range) >> >> start = range->start >> sb->s_blocksize_bits; >> end = start + (range->len >> sb->s_blocksize_bits) - 1; >> - minlen = EXT4_NUM_B2C(EXT4_SB(sb), >> - range->minlen >> sb->s_blocksize_bits); >> + minlen = (range->minlen + EXT4_CLUSTER_SIZE(sb) - 1) >> >> + (sb->s_blocksize_bits + EXT4_CLUSTER_BITS(sb)); >> >> if (minlen > EXT4_CLUSTERS_PER_GROUP(sb) || >> start >= max_blks || >> -- >> 2.25.1 >>
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