[PATCH 5.4 022/215] ext4: correct best extent lstart adjustment logic

Greg Kroah-Hartman
2024-04-11T10:17:30Z

From: Baokun Li <libaokun1@huawei.com>

[ Upstream commit 4fbf8bc733d14bceb16dda46a3f5e19c6a9621c5 ]

When yangerkun review commit 93cdf49f6eca ("ext4: Fix best extent lstart
adjustment logic in ext4_mb_new_inode_pa()"), it was found that the best
extent did not completely cover the original request after adjusting the
best extent lstart in ext4_mb_new_inode_pa() as follows:

original request: 2/10(8)
normalized request: 0/64(64)
best extent: 0/9(9)

When we check if best ex can be kept at start of goal, ac_o_ex.fe_logical
is 2 less than the adjusted best extent logical end 9, so we think the
adjustment is done. But obviously 0/9(9) doesn't cover 2/10(8), so we
should determine here if the original request logical end is less than or
equal to the adjusted best extent logical end.

In addition, add a comment stating when adjusted best_ex will not cover
the original request, and remove the duplicate assertion because adjusting
lstart makes no change to b_ex.fe_len.

Link: https://lore.kernel.org/r/3630fa7f-b432-7afd-5f79-781bc3b2c5ea@huawei.com
Fixes: 93cdf49f6eca ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
Cc: <stable@kernel.org>
Signed-off-by: yangerkun <yangerkun@huawei.com>
Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20240201141845.1879253-1-libaokun1@huawei.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/ext4/mballoc.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index e823731110e3e..b2e7b1907d410 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -3692,10 +3692,16 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
.fe_len = ac->ac_g_ex.fe_len,
};
loff_t orig_goal_end = extent_logical_end(sbi, &ex);
+ loff_t o_ex_end = extent_logical_end(sbi, &ac->ac_o_ex);

- /* we can't allocate as much as normalizer wants.
- * so, found space must get proper lstart
- * to cover original request */
+ /*
+ * We can't allocate as much as normalizer wants, so we try
+ * to get proper lstart to cover the original request, except
+ * when the goal doesn't cover the original request as below:
+ *
+ * orig_ex:2045/2055(10), isize:8417280 -> normalized:0/2048
+ * best_ex:0/200(200) -> adjusted: 1848/2048(200)
+ */
BUG_ON(ac->ac_g_ex.fe_logical > ac->ac_o_ex.fe_logical);
BUG_ON(ac->ac_g_ex.fe_len < ac->ac_o_ex.fe_len);

@@ -3707,7 +3713,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
* 1. Check if best ex can be kept at end of goal and still
* cover original start
* 2. Else, check if best ex can be kept at start of goal and
- * still cover original start
+ * still cover original end
* 3. Else, keep the best ex at start of original request.
*/
ex.fe_len = ac->ac_b_ex.fe_len;
@@ -3717,7 +3723,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
goto adjust_bex;

ex.fe_logical = ac->ac_g_ex.fe_logical;
- if (ac->ac_o_ex.fe_logical < extent_logical_end(sbi, &ex))
+ if (o_ex_end <= extent_logical_end(sbi, &ex))
goto adjust_bex;

ex.fe_logical = ac->ac_o_ex.fe_logical;
@@ -3725,7 +3731,6 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac)
ac->ac_b_ex.fe_logical = ex.fe_logical;

BUG_ON(ac->ac_o_ex.fe_logical < ac->ac_b_ex.fe_logical);
- BUG_ON(ac->ac_o_ex.fe_len > ac->ac_b_ex.fe_len);
BUG_ON(extent_logical_end(sbi, &ex) > orig_goal_end);
}

--
2.43.0