FAILED: patch "[PATCH] ext4: fix race when setting the bitmap corrupted flag" failed to apply to 4.9-stable tree

[<gregkh@xxxxxxxxxxxxxxxxxxx>]

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm
tree, then please email the backport, including the original git commit
id to <stable@xxxxxxxxxxxxxxx>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

>From 9af0b3d1257756394ebbd06b14937b557e3a756b Mon Sep 17 00:00:00 2001
From: Wang Shilong <wshilong@xxxxxxx>
Date: Sun, 29 Jul 2018 17:27:45 -0400
Subject: [PATCH] ext4: fix race when setting the bitmap corrupted flag

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@xxxxxxx>
Signed-off-by: Theodore Ts'o <tytso@xxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index d4a218ba626c..f7750bc5b85a 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -795,26 +795,26 @@ 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);
 	}
 }