xfs: reduce ilock acquisitions in xfs_file_fsync

If the inode is not pinned by the time fsync is called we don't need the
ilock to protect against concurrent clearing of ili_fsync_fields as the
inode won't need a log flush or clearing of these fields.  Not taking
the iolock allows for full concurrency of fsync and thus O_DSYNC
completions with io_uring/aio write submissions.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

fs/xfs/xfs_file.c

@@ -200,7 +200,14 @@ xfs_file_fsync(
 	else if (mp->m_logdev_targp != mp->m_ddev_targp)
 		xfs_blkdev_issue_flush(mp->m_ddev_targp);
 
-	error = xfs_fsync_flush_log(ip, datasync, &log_flushed);
+	/*
+	 * Any inode that has dirty modifications in the log is pinned.  The
+	 * racy check here for a pinned inode while not catch modifications
+	 * that happen concurrently to the fsync call, but fsync semantics
+	 * only require to sync previously completed I/O.
+	 */
+	if (xfs_ipincount(ip))
+		error = xfs_fsync_flush_log(ip, datasync, &log_flushed);
 
 	/*
 	 * If we only have a single device, and the log force about was