btrfs: set BTRFS_FS_STATE_NO_CSUMS if we fail to load the csum root

We have a few places where we skip doing csums if we mounted with one of
the rescue options that ignores bad csum roots.  In the future when
there are multiple csum roots it'll be costly to check and see if there
are any missing csum roots, so simply add a flag to indicate the fs
should skip loading csums in case of errors.
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/compression.c

@@ -157,7 +157,8 @@ static int check_compressed_csum(struct btrfs_inode *inode, struct bio *bio,
 	struct compressed_bio *cb = bio->bi_private;
 	u8 *cb_sum = cb->sums;
 
-	if (!fs_info->csum_root || (inode->flags & BTRFS_INODE_NODATASUM))
+	if ((inode->flags & BTRFS_INODE_NODATASUM) ||
+	    test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state))
 		return 0;
 
 	shash->tfm = fs_info->csum_shash;

fs/btrfs/ctree.h

@@ -143,6 +143,8 @@ enum {
 	BTRFS_FS_STATE_DEV_REPLACING,
 	/* The btrfs_fs_info created for self-tests */
 	BTRFS_FS_STATE_DUMMY_FS_INFO,
+
+	BTRFS_FS_STATE_NO_CSUMS,
 };
 
 #define BTRFS_BACKREF_REV_MAX		256

fs/btrfs/disk-io.c

@@ -2482,11 +2482,16 @@ static int btrfs_read_roots(struct btrfs_fs_info *fs_info)
 			if (!btrfs_test_opt(fs_info, IGNOREBADROOTS)) {
 				ret = PTR_ERR(root);
 				goto out;
+			} else {
+				set_bit(BTRFS_FS_STATE_NO_CSUMS,
+					&fs_info->fs_state);
 			}
 		} else {
 			set_bit(BTRFS_ROOT_TRACK_DIRTY, &root->state);
 			fs_info->csum_root = root;
 		}
+	} else {
+		set_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state);
 	}
 
 	/*

fs/btrfs/file-item.c

@@ -376,7 +376,8 @@ blk_status_t btrfs_lookup_bio_sums(struct inode *inode, struct bio *bio, u8 *dst
 	const unsigned int nblocks = orig_len >> fs_info->sectorsize_bits;
 	int count = 0;
 
-	if (!fs_info->csum_root || (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM))
+	if ((BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM) ||
+	    test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state))
 		return BLK_STS_OK;
 
 	/*

fs/btrfs/inode.c

@@ -2516,7 +2516,7 @@ blk_status_t btrfs_submit_data_bio(struct inode *inode, struct bio *bio,
 	int async = !atomic_read(&BTRFS_I(inode)->sync_writers);
 
 	skip_sum = (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM) ||
-		   !fs_info->csum_root;
+		test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state);
 
 	if (btrfs_is_free_space_inode(BTRFS_I(inode)))
 		metadata = BTRFS_WQ_ENDIO_FREE_SPACE;
@@ -3314,7 +3314,7 @@ unsigned int btrfs_verify_data_csum(struct btrfs_bio *bbio,
 	if (BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM)
 		return 0;
 
-	if (!root->fs_info->csum_root)
+	if (unlikely(test_bit(BTRFS_FS_STATE_NO_CSUMS, &fs_info->fs_state)))
 		return 0;
 
 	ASSERT(page_offset(page) <= start &&