Commit 4fbf8bc7 authored by Baokun Li's avatar Baokun Li Committed by Theodore Ts'o
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ext4: correct best extent lstart adjustment logic 

When yangerkun review commit 93cdf49f ("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: 93cdf49f ("ext4: Fix best extent lstart adjustment logic in ext4_mb_new_inode_pa()")
Cc:  <stable@kernel.org>
Signed-off-by: default avataryangerkun <yangerkun@huawei.com>
Signed-off-by: default avatarBaokun Li <libaokun1@huawei.com>
Reviewed-by: default avatarJan Kara <jack@suse.cz>
Reviewed-by: default avatarOjaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20240201141845.1879253-1-libaokun1@huawei.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent d8b945fa

fs/ext4/mballoc.c

+11 −6
Original line number Diff line number Diff line
@@ -5172,10 +5172,16 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac) 
			.fe_len = ac->ac_orig_goal_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);
@@ -5187,7 +5193,7 @@ ext4_mb_new_inode_pa(struct ext4_allocation_context *ac) 
		 * 1. Check if best ex can be kept at end of goal (before

		 *    cr_best_avail trimmed it) 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;
@@ -5197,7 +5203,7 @@ 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;
@@ -5205,7 +5211,6 @@ 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);

	}