Mailing List Archive

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@mit.edu>
Signed-off-by: Chao Yu <chao@kernel.org>
---
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