linux-ext4 - [PATCH 8/8] ext4: try all groups in ext4_mb_new_blocks

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Date:   Wed, 22 Mar 2023 00:12:20 +0800
From:   Kemeng Shi <shikemeng@...weicloud.com>
To:     tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     ojaswin@...ux.ibm.com, shikemeng@...weicloud.com
Subject: [PATCH 8/8] ext4: try all groups in ext4_mb_new_blocks_simple

ext4_mb_new_blocks_simple ignores the group before goal, so it will fail
if free blocks reside in group before goal. Try all groups to avoid
unexpected failure.
Search finishes either if any free block is found or if no available
blocks are found. Simpliy check "i >= max" to distinguish the above
cases.

Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
Suggested-by: Theodore Ts'o <tytso@....edu>
---
 fs/ext4/mballoc.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5b837918c624..ee564e700278 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -5796,7 +5796,7 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 	struct buffer_head *bitmap_bh;
 	struct super_block *sb = ar->inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	ext4_group_t group;
+	ext4_group_t group, nr;
 	ext4_grpblk_t blkoff;
 	ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
 	ext4_grpblk_t i = 0;
@@ -5810,7 +5810,7 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 
 	ar->len = 0;
 	ext4_get_group_no_and_offset(sb, goal, &group, &blkoff);
-	for (; group < ext4_get_groups_count(sb); group++) {
+	for (nr = ext4_get_groups_count(sb); nr > 0; nr--) {
 		bitmap_bh = ext4_read_block_bitmap(sb, group);
 		if (IS_ERR(bitmap_bh)) {
 			*errp = PTR_ERR(bitmap_bh);
@@ -5834,10 +5834,13 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 		if (i < max)
 			break;
 
+		if (++group >= ext4_get_groups_count(sb))
+			group = 0;
+
 		blkoff = 0;
 	}
 
-	if (group >= ext4_get_groups_count(sb) || i >= max) {
+	if (i >= max) {
 		*errp = -ENOSPC;
 		return 0;
 	}
-- 
2.30.0