generic: Add regression test for tail page zeroing

Add test checking for a race in ext4 writeback that could result in
zeroing too much from the tail page during writeback.

[eguan: removed from quick group, it needs longer time on xfs and
btrfs]

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

.gitignore

@@ -150,6 +150,7 @@
 /src/t_mmap_dio
 /src/t_mmap_stale_pmd
 /src/t_mmap_cow_race
+/src/t_mmap_fallocate
 
 # dmapi/ binaries
 /dmapi/src/common/cmd/read_invis

src/Makefile

@@ -13,7 +13,7 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
 	multi_open_unlink dmiperf unwritten_sync genhashnames t_holes \
 	t_mmap_writev t_truncate_cmtime dirhash_collide t_rename_overwrite \
 	holetest t_truncate_self t_mmap_dio af_unix t_mmap_stale_pmd \
-	t_mmap_cow_race
+	t_mmap_cow_race t_mmap_fallocate
 
 LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	preallo_rw_pattern_writer ftrunc trunc fs_perms testx looptest \

src/t_mmap_fallocate.c

@@ -0,0 +1,69 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <libgen.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+int main(int argc, char **argv)
+{
+	int fd;
+	char *buf;
+	size_t fsize, i;
+
+	if (argc != 3) {
+		fprintf(stderr, "Usage: %s <file> <size-in-KB>\n",
+			basename(argv[0]));
+		exit(1);
+	}
+
+	fsize = strtol(argv[2], NULL, 10);
+	if (fsize <= 0) {
+		fprintf(stderr, "Invalid file size: %s\n", argv[2]);
+		exit(1);
+	}
+	fsize <<= 10;
+
+	fd = open(argv[1], O_RDWR | O_CREAT | O_TRUNC, 0644);
+	if (fd < 0) {
+		perror("Cannot open file");
+	        exit(1);
+	}
+
+	buf = mmap(NULL, fsize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
+	if (buf == MAP_FAILED) {
+		perror("Cannot memory map");
+		exit(1);
+	}
+
+	/*
+	 * We extend the file byte-by-byte through fallocate(2) and write data
+	 * to each byte through the mmap. Then we verify whether the data is
+	 * really there to see whether the zeroing of last file page during
+	 * writeback didn't corrupt the data.
+	 */
+	for (i = 0; i < fsize; i++) {
+		if (posix_fallocate(fd, i, 1) != 0) {
+			perror("Cannot fallocate");
+			exit(1);
+		}
+		buf[i] = 0x78;
+
+		if (buf[i] != 0x78) {
+			fprintf(stderr,
+				"Value not written correctly (off=%lu)\n",
+				(unsigned long)i);
+			exit(1);
+		}
+	}
+
+	for (i = 0; i < fsize; i++) {
+		if (buf[i] != 0x78) {
+			fprintf(stderr, "Value has been modified (off=%lu)\n",
+				(unsigned long)i);
+			exit(1);
+		}
+	}
+
+	return 0;
+}

tests/generic/438

@@ -0,0 +1,82 @@
+#! /bin/bash
+# FS QA Test 438
+#
+# This is a regression test for kernel patch
+#   "ext4: Fix data corruption for mmap writes"
+#
+# The problem this test checks for is when too much is zeroed in the tail
+# page that gets written out just while the file gets extended and written
+# to through mmap.
+#
+# Based on test program by Michael Zimmer <michael@swarm64.com>
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2017 SUSE.  All Rights Reserved.
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it would be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write the Free Software Foundation,
+# Inc.,  51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+#-----------------------------------------------------------------------
+#
+
+seq=`basename $0`
+seqres=$RESULT_DIR/$seq
+echo "QA output created by $seq"
+
+here=`pwd`
+tmp=/tmp/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	rm -f $FILE
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# Modify as appropriate.
+_supported_fs generic
+_supported_os Linux
+_require_test
+_require_test_program "t_mmap_fallocate"
+
+# real QA test starts here
+FILE=$TEST_DIR/testfile_fallocate
+# Make sure file exists
+echo >$FILE
+# Force frequent writeback of the file
+(
+	trap "STOP=1" SIGTERM
+	STOP=0
+	while [ $STOP -eq 0 ]; do
+		$XFS_IO_PROG -c fsync $FILE
+	done
+)&
+SYNCPID=$!
+
+# Run the test
+src/t_mmap_fallocate $FILE 256 && echo "Silence is golden"
+
+kill -TERM $SYNCPID
+wait $SYNCPID
+
+# success, all done
+status=0
+exit

tests/generic/438.out

@@ -0,0 +1,2 @@
+QA output created by 438
+Silence is golden

tests/generic/group

@@ -440,3 +440,4 @@
 435 auto encrypt
 436 auto quick rw
 437 auto quick
+438 auto