[PATCH RFC 2/9] ext2: don't read the inode block in ext2_sync_inode_metadata()

[Christian Brauner <brauner@kernel.org>]

ext2_sync_inode_metadata() looks up the inode block with
ext2_get_inode() which reads it from disk if it isn't cached. But a
block that isn't in the buffer cache is neither dirty nor under
writeback. So there's nothing to write or to wait for and reading it in
is pointless.

It's also not something we can afford once inode eviction calls
->sync_inode_metadata() from reclaim. So look the block up with
sb_find_get_block_nonatomic() instead, the same way
fat_sync_inode_metadata() already does.

Cc: stable@vger.kernel.org # v7.3
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/ext2/inode.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 940f61a4dde3..efb50cb48da3 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -1586,19 +1586,22 @@ int ext2_write_inode(struct inode *inode, struct writeback_control *wbc)
 int ext2_sync_inode_metadata(struct inode *inode, struct writeback_control *wbc)
 {
 	struct buffer_head *bh;
-	struct ext2_inode *raw_inode = ext2_get_inode(inode->i_sb, inode->i_ino,
-						      &bh);
+	unsigned long block, offset;
 	int err = 0;
 
-	if (IS_ERR(raw_inode))
+	if (ext2_inode_block(inode->i_sb, inode->i_ino, &block, &offset))
 		return -EIO;
 	err = mmb_sync(&EXT2_I(inode)->i_metadata_bhs);
 	if (err) {
 		ext2_error(inode->i_sb, __func__,
 			"Error syncing inode metadata ino=%lu\n",
 			(unsigned long)inode->i_ino);
-		goto out;
+		return err;
 	}
+	/* A block that isn't cached is neither dirty nor under writeback. */
+	bh = sb_find_get_block_nonatomic(inode->i_sb, block);
+	if (!bh)
+		return 0;
 	sync_dirty_buffer(bh);
 	if (buffer_write_io_error(bh)) {
 		ext2_error(inode->i_sb, __func__,
@@ -1606,7 +1609,6 @@ int ext2_sync_inode_metadata(struct inode *inode, struct writeback_control *wbc)
 			(unsigned long)inode->i_ino);
 		err = -EIO;
 	}
-out:
 	brelse(bh);
 	return err;
 }

-- 
2.53.0