ext4: revert commit which was causing fs corruption after journal replays

Commit 0076493 ("ext4: initialize multi-block allocator before
checking block descriptors") causes the block group descriptor's count
of the number of free blocks to become inconsistent with the number of
free blocks in the allocation bitmap.  This is a harmless form of fs
corruption, but it causes the kernel to potentially remount the file
system read-only, or to panic, depending on the file systems's error
behavior.

Thanks to Eric Whitney for his tireless work to reproduce and to find
the guilty commit.

Fixes: 0076493 ("ext4: initialize multi-block allocator before checking block descriptors"

Cc: [email protected]  # 3.15
Reported-by: David Jander <[email protected]>
Reported-by: Matteo Croce <[email protected]>
Tested-by: Eric Whitney <[email protected]>
Suggested-by: Eric Whitney <[email protected]>
Signed-off-by: Theodore Ts'o <[email protected]>

Author: tytso

fs/ext4/super.c

@@ -3879,38 +3879,19 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 			goto failed_mount2;
 		}
 	}
-
-	/*
-	 * set up enough so that it can read an inode,
-	 * and create new inode for buddy allocator
-	 */
-	sbi->s_gdb_count = db_count;
-	if (!test_opt(sb, NOLOAD) &&
-	    EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_HAS_JOURNAL))
-		sb->s_op = &ext4_sops;
-	else
-		sb->s_op = &ext4_nojournal_sops;
-
-	ext4_ext_init(sb);
-	err = ext4_mb_init(sb);
-	if (err) {
-		ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
-			 err);
-		goto failed_mount2;
-	}
-
 	if (!ext4_check_descriptors(sb, &first_not_zeroed)) {
 		ext4_msg(sb, KERN_ERR, "group descriptors corrupted!");
-		goto failed_mount2a;
+		goto failed_mount2;
 	}
 	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG))
 		if (!ext4_fill_flex_info(sb)) {
 			ext4_msg(sb, KERN_ERR,
 			       "unable to initialize "
 			       "flex_bg meta info!");
-			goto failed_mount2a;
+			goto failed_mount2;
 		}
 
+	sbi->s_gdb_count = db_count;
 	get_random_bytes(&sbi->s_next_generation, sizeof(u32));
 	spin_lock_init(&sbi->s_next_gen_lock);
 
@@ -3945,6 +3926,14 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	sbi->s_stripe = ext4_get_stripe_size(sbi);
 	sbi->s_extent_max_zeroout_kb = 32;
 
+	/*
+	 * set up enough so that it can read an inode
+	 */
+	if (!test_opt(sb, NOLOAD) &&
+	    EXT4_HAS_COMPAT_FEATURE(sb, EXT4_FEATURE_COMPAT_HAS_JOURNAL))
+		sb->s_op = &ext4_sops;
+	else
+		sb->s_op = &ext4_nojournal_sops;
 	sb->s_export_op = &ext4_export_ops;
 	sb->s_xattr = ext4_xattr_handlers;
 #ifdef CONFIG_QUOTA
@@ -4134,13 +4123,21 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	if (err) {
 		ext4_msg(sb, KERN_ERR, "failed to reserve %llu clusters for "
 			 "reserved pool", ext4_calculate_resv_clusters(sb));
-		goto failed_mount5;
+		goto failed_mount4a;
 	}
 
 	err = ext4_setup_system_zone(sb);
 	if (err) {
 		ext4_msg(sb, KERN_ERR, "failed to initialize system "
 			 "zone (%d)", err);
+		goto failed_mount4a;
+	}
+
+	ext4_ext_init(sb);
+	err = ext4_mb_init(sb);
+	if (err) {
+		ext4_msg(sb, KERN_ERR, "failed to initialize mballoc (%d)",
+			 err);
 		goto failed_mount5;
 	}
 
@@ -4217,8 +4214,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 failed_mount7:
 	ext4_unregister_li_request(sb);
 failed_mount6:
-	ext4_release_system_zone(sb);
+	ext4_mb_release(sb);
 failed_mount5:
+	ext4_ext_release(sb);
+	ext4_release_system_zone(sb);
+failed_mount4a:
 	dput(sb->s_root);
 	sb->s_root = NULL;
 failed_mount4:
@@ -4242,14 +4242,11 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	percpu_counter_destroy(&sbi->s_extent_cache_cnt);
 	if (sbi->s_mmp_tsk)
 		kthread_stop(sbi->s_mmp_tsk);
-failed_mount2a:
-	ext4_mb_release(sb);
 failed_mount2:
 	for (i = 0; i < db_count; i++)
 		brelse(sbi->s_group_desc[i]);
 	ext4_kvfree(sbi->s_group_desc);
 failed_mount:
-	ext4_ext_release(sb);
 	if (sbi->s_chksum_driver)
 		crypto_free_shash(sbi->s_chksum_driver);
 	if (sbi->s_proc) {