linux-ext4 - [PATCH 1/5] ext4: fix race with setting free_inode/clusters

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Date:   Tue, 29 May 2018 20:45:13 +0900
From:   Wang Shilong <wangshilong1991@...il.com>
To:     linux-ext4@...r.kernel.org
Cc:     andreas.dilger@...el.com, sihara@....com, wshilong@....com
Subject: [PATCH 1/5] ext4: fix race with setting free_inode/clusters_counter

From: Wang Shilong <wshilong@....com>

Whenever we hit block or inode bitmap corruptions we set
bit and then reduce this block group free inode/clusters
counter to expose right available space.

However some of ext4_mark_group_bitmap_corrupted() is called
inside group spinlock, some are not, this could make it happen
that we double reduce one block group free counters from system.

Always hold group spinlock for it could fix it, but it looks
a little heavy, we could use test_and_set_bit() to fix race
problems here.

Signed-off-by: Wang Shilong <wshilong@....com>
---
 fs/ext4/super.c | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index c1c5c87..d6fa6cf 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -770,26 +770,26 @@ void ext4_mark_group_bitmap_corrupted(struct super_block *sb,
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_group_info *grp = ext4_get_group_info(sb, group);
 	struct ext4_group_desc *gdp = ext4_get_group_desc(sb, group, NULL);
+	int ret;
 
-	if ((flags & EXT4_GROUP_INFO_BBITMAP_CORRUPT) &&
-	    !EXT4_MB_GRP_BBITMAP_CORRUPT(grp)) {
-		percpu_counter_sub(&sbi->s_freeclusters_counter,
-					grp->bb_free);
-		set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT,
-			&grp->bb_state);
+	if (flags & EXT4_GROUP_INFO_BBITMAP_CORRUPT) {
+		ret = ext4_test_and_set_bit(EXT4_GROUP_INFO_BBITMAP_CORRUPT_BIT,
+					    &grp->bb_state);
+		if (!ret)
+			percpu_counter_sub(&sbi->s_freeclusters_counter,
+					   grp->bb_free);
 	}
 
-	if ((flags & EXT4_GROUP_INFO_IBITMAP_CORRUPT) &&
-	    !EXT4_MB_GRP_IBITMAP_CORRUPT(grp)) {
-		if (gdp) {
+	if (flags & EXT4_GROUP_INFO_IBITMAP_CORRUPT) {
+		ret = ext4_test_and_set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT,
+					    &grp->bb_state);
+		if (!ret && gdp) {
 			int count;
 
 			count = ext4_free_inodes_count(sb, gdp);
 			percpu_counter_sub(&sbi->s_freeinodes_counter,
 					   count);
 		}
-		set_bit(EXT4_GROUP_INFO_IBITMAP_CORRUPT_BIT,
-			&grp->bb_state);
 	}
 }
 
-- 
1.8.3.1