From 5d5460fa7932bed3a9082a6a8852cfbdb46acbe8 Mon Sep 17 00:00:00 2001
From: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Date: Fri, 9 Jun 2023 16:04:03 +0530
Subject: [PATCH] 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: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230609103403.112807-1-ojaswin@linux.ibm.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
---
fs/ext4/mballoc.c | 14 +++++++++-----
1 file changed, 9 insertions(+), 5 deletions(-)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index a2475b8c9fb5f..456150ef6111c 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -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;
/*
--
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