linux-ext4 - [RFC 03/11] ext4: mballoc: Fix getting the right group desc in ext4_mb_prefetch

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Message-Id: <85bbcb3774e38de65b737ef0000241ddbdda73aa.1674822311.git.ojaswin@linux.ibm.com>
Date:   Fri, 27 Jan 2023 18:07:30 +0530
From:   Ojaswin Mujoo <ojaswin@...ux.ibm.com>
To:     linux-ext4@...r.kernel.org, "Theodore Ts'o" <tytso@....edu>
Cc:     Ritesh Harjani <riteshh@...ux.ibm.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>, Ritesh Harjani <ritesh.list@...il.com>
Subject: [RFC 03/11] ext4: mballoc: Fix getting the right group desc in ext4_mb_prefetch_fini

group descriptor and group info are not of the same group in
ext4_mb_prefetch_fini(). This problem was found during code
review/walkthrough and seems like a bug, so fix it.

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@...il.com>
Signed-off-by: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
---
 fs/ext4/mballoc.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 572e79a698d4..8b22cc07b054 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2569,14 +2569,14 @@ ext4_group_t ext4_mb_prefetch(struct super_block *sb, ext4_group_t group,
 void ext4_mb_prefetch_fini(struct super_block *sb, ext4_group_t group,
 			   unsigned int nr)
 {
-	while (nr-- > 0) {
-		struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group,
-								  NULL);
-		struct ext4_group_info *grp = ext4_get_group_info(sb, group);
+	struct ext4_group_desc *gdp;
+	struct ext4_group_info *grp;
 
+	while (nr-- > 0) {
 		if (!group)
 			group = ext4_get_groups_count(sb);
 		group--;
+		gdp = ext4_get_group_desc(sb, group, NULL);
 		grp = ext4_get_group_info(sb, group);
 
 		if (EXT4_MB_GRP_NEED_INIT(grp) &&
-- 
2.31.1