generic/608: Add new regression test

Write data into a file and then enable DAX on the file immediately,
the written data which is still in the buffer should be synchronized
to disk instead of discarded when the corresponding inode is evicted.

It's a regression test for commit 88149082bb8e ("fs: Handle
I_DONTCACHE in iput_final() instead of generic_drop_inode()")

Signed-off-by: Xiao Yang <yangx.jy@fujitsu.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/608

@@ -7,6 +7,12 @@
 # file change immediately when all applications close the file.
 # It's a regression test for:
 # 'commit 77573fa310d9 ("fs: Kill DCACHE_DONTCACHE dentry even if DCACHE_REFERENCED is set")'
+#
+# Write data into a file and then enable DAX on the file immediately,
+# the written data which is still in the buffer should be synchronized
+# to disk instead of discarded when the corresponding inode is evicted.
+# It's a regression test for:
+# 'commit 88149082bb8e ("fs: Handle I_DONTCACHE in iput_final() instead of generic_drop_inode()"'
 
 seq=`basename $0`
 seqres=$RESULT_DIR/$seq
@@ -87,6 +93,26 @@ test_disable_dax()
 	_check_s_dax $t_file 0
 }
 
+test_buffered_data_lost()
+{
+	local t_file=$SCRATCH_MNT/datafile
+
+	# Write data into a file
+	echo "Buffered data" > $t_file
+
+	# Then enable DAX on the file immediately
+	$XFS_IO_PROG -c 'chattr +x' $t_file
+
+	# Without commit 77573fa310d9, ensure inode can
+	# be evicted by drop_caches
+	echo 2 > /proc/sys/vm/drop_caches
+
+	# The written data which is still in the buffer should not be lost
+	grep -q "Buffered data" $t_file || echo "Buffered data is lost"
+
+	rm -f $t_file
+}
+
 do_tests()
 {
 	local mount_option=$1
@@ -100,6 +126,9 @@ do_tests()
 	test_enable_dax
 	test_disable_dax
 
+	# Do test for commit 88149082bb8e
+	test_buffered_data_lost
+
 	_scratch_unmount
 }