[PATCH RFC 7/9] udf: don't allocate the inode block in udf_sync_inode_metadata()

[Christian Brauner <brauner@kernel.org>]

udf_sync_inode_metadata() looks up the block that holds the inode with
sb_getblk() which allocates a buffer for it 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 allocating a
buffer that just gets thrown away again 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.

Cc: stable@vger.kernel.org # v7.3
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
---
 fs/udf/inode.c | 27 +++++++++++++--------------
 1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/fs/udf/inode.c b/fs/udf/inode.c
index bacf2a86161e..59f8e9bde0b1 100644
--- a/fs/udf/inode.c
+++ b/fs/udf/inode.c
@@ -1744,23 +1744,22 @@ int udf_sync_inode_metadata(struct inode *inode, struct writeback_control *wbc)
 	struct buffer_head *bh;
 	int err = 0;
 
-	bh = sb_getblk(inode->i_sb,
+	/* A block that isn't cached is neither dirty nor under writeback. */
+	bh = sb_find_get_block_nonatomic(inode->i_sb,
 			udf_get_lb_pblock(inode->i_sb,
 					  &UDF_I(inode)->i_location, 0));
-	if (!bh)
-		return -EIO;
-
-	sync_dirty_buffer(bh);
-	if (buffer_write_io_error(bh)) {
-		udf_warn(inode->i_sb, "IO error syncing udf inode [%08llx]\n",
-			 inode->i_ino);
-		err = -EIO;
-		goto out;
+	if (bh) {
+		sync_dirty_buffer(bh);
+		if (buffer_write_io_error(bh)) {
+			udf_warn(inode->i_sb, "IO error syncing udf inode [%08llx]\n",
+				 inode->i_ino);
+			err = -EIO;
+		}
+		brelse(bh);
+		if (err)
+			return err;
 	}
-	err = mmb_sync(&UDF_I(inode)->i_metadata_bhs);
-out:
-	brelse(bh);
-	return err;
+	return mmb_sync(&UDF_I(inode)->i_metadata_bhs);
 }
 
 static void udf_adjust_time(struct udf_inode_info *iinfo, struct timespec64 time)

-- 
2.53.0