Commit 5d5460fa authored by Ojaswin Mujoo's avatar Ojaswin Mujoo Committed by Theodore Ts'o
Browse files

ext4: fix off by one issue in ext4_mb_choose_next_group_best_avail() 



In ext4_mb_choose_next_group_best_avail(), we want the start order to be
1 less than goal length and the min_order to be, at max, 1 more than the
original length. This commit fixes an off by one issue that arose due to
the fact that 1 << fls(n) > (n).

After all the processing:

order = 1 order below goal len
min_order = maximum of the three:-
             - order - trim_order
             - 1 order below B2C(s_stripe)
             - 1 order above original len

Cc: stable@kernel.org
Fixes: 33122aa930 ("ext4: Add allocation criteria 1.5 (CR1_5)")
Signed-off-by: default avatarOjaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230609103403.112807-1-ojaswin@linux.ibm.com


Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent 6909cf5c

fs/ext4/mballoc.c

+9 −5
Original line number Diff line number Diff line
@@ -1006,14 +1006,11 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context 
	 * fls() instead since we need to know the actual length while modifying

	 * goal length.

	 */

	order = fls(ac->ac_g_ex.fe_len);

	order = fls(ac->ac_g_ex.fe_len) - 1;

	min_order = order - sbi->s_mb_best_avail_max_trim_order;

	if (min_order < 0)

		min_order = 0;



	if (1 << min_order < ac->ac_o_ex.fe_len)

		min_order = fls(ac->ac_o_ex.fe_len) + 1;



	if (sbi->s_stripe > 0) {

		/*

		 * We are assuming that stripe size is always a multiple of
@@ -1021,9 +1018,16 @@ static void ext4_mb_choose_next_group_best_avail(struct ext4_allocation_context 
		 */

		num_stripe_clusters = EXT4_NUM_B2C(sbi, sbi->s_stripe);

		if (1 << min_order < num_stripe_clusters)

			min_order = fls(num_stripe_clusters);

			/*

			 * We consider 1 order less because later we round

			 * up the goal len to num_stripe_clusters

			 */

			min_order = fls(num_stripe_clusters) - 1;

	}



	if (1 << min_order < ac->ac_o_ex.fe_len)

		min_order = fls(ac->ac_o_ex.fe_len);



	for (i = order; i >= min_order; i--) {

		int frag_order;

		/*