[PATCH] generic/639: Test page faults during read and write

[Andreas Gruenbacher <agruenba@redhat.com>]

Some filesystems have problems when the buffer passed to read or write is
memory-mapped to the file being read from or written to and the buffer is
faulted in during the read or write.  (That's probably not a recommended
use case, but it should work nevertheless.)

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 src/Makefile          |   2 +-
 src/mmap-rw-fault.c   | 169 ++++++++++++++++++++++++++++++++++++++++++
 tests/generic/639     |  40 ++++++++++
 tests/generic/639.out |   2 +
 tests/generic/group   |   1 +
 5 files changed, 213 insertions(+), 1 deletion(-)
 create mode 100644 src/mmap-rw-fault.c
 create mode 100755 tests/generic/639
 create mode 100644 tests/generic/639.out

diff --git a/src/Makefile b/src/Makefile
index 1279e4b9..6e3871b9 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -18,7 +18,7 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
 	t_ext4_dax_journal_corruption t_ext4_dax_inline_corruption \
 	t_ofd_locks t_mmap_collision mmap-write-concurrent \
 	t_get_file_time t_create_short_dirs t_create_long_dirs t_enospc \
-	t_mmap_writev_overlap
+	t_mmap_writev_overlap mmap-rw-fault
 
 LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	preallo_rw_pattern_writer ftrunc trunc fs_perms testx looptest \
diff --git a/src/mmap-rw-fault.c b/src/mmap-rw-fault.c
new file mode 100644
index 00000000..31778769
--- /dev/null
+++ b/src/mmap-rw-fault.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Trigger mmap page faults in the same file during pread and pwrite.
+ * Copyright (C) 2021 Red Hat, Inc. All Rights Reserved.
+ * Written by Andreas Gruenbacher <agruenba@redhat.com>
+ */
+
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE /* to get definition of O_DIRECT flag. */
+#endif
+
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <sys/mman.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <errno.h>
+#include <err.h>
+
+char *filename;
+unsigned int page_size;
+void *page;
+char *addr;
+int fd;
+ssize_t ret;
+
+/*
+ * Leave a hole at the beginning of the test file and initialize a block of
+ * @page_size bytes at offset @page_size to @c.  Then, reopen the file and
+ * mmap the first two pages.
+ */
+void init(char c, int flags)
+{
+	fd = open(filename, O_CREAT | O_TRUNC | O_WRONLY | O_DIRECT, 0666);
+	if (fd == -1)
+		goto fail;
+	memset(page, c, page_size);
+	ret = pwrite(fd, page, page_size, page_size);
+	if (ret != page_size)
+		goto fail;
+	if (close(fd))
+		goto fail;
+
+	fd = open(filename, flags);
+	if (fd == -1)
+		goto fail;
+	addr = mmap(NULL, 2 * page_size, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
+	if (addr == MAP_FAILED)
+		err(1, NULL);
+	return;
+
+fail:
+	err(1, "%s", filename);
+}
+
+void done(void)
+{
+	if (fsync(fd))
+		goto fail;
+	if (close(fd))
+		goto fail;
+	return;
+
+fail:
+	err(1, "%s", filename);
+}
+
+static ssize_t do_read(int fd, void *buf, size_t count, off_t offset)
+{
+	ssize_t count2 = 0, ret;
+
+	do {
+		ret = pread(fd, buf, count, offset);
+		if (ret == -1) {
+			if (errno == EINTR)
+				continue;
+			break;
+		}
+		if (ret == 0)
+			break;
+		count2 += ret;
+		buf += ret;
+		count -= ret;
+	} while (count);
+	return count2;
+}
+
+static ssize_t do_write(int fd, const void *buf, size_t count, off_t offset)
+{
+	ssize_t count2 = 0, ret;
+
+	do {
+		ret = pwrite(fd, buf, count, offset);
+		if (ret == -1) {
+			if (errno == EINTR)
+				continue;
+			break;
+		}
+		if (ret == 0)
+			break;
+		count2 += ret;
+		buf += ret;
+		count -= ret;
+	} while (count);
+	return count2;
+}
+
+int main(int argc, char *argv[])
+{
+	if (argc != 2)
+		errx(1, "no test filename argument given");
+	filename = argv[1];
+
+	page_size = ret = sysconf(_SC_PAGE_SIZE);
+	if (ret == -1)
+		err(1, NULL);
+
+	ret = posix_memalign(&page, page_size, page_size);
+	if (ret) {
+		errno = ENOMEM;
+		err(1, NULL);
+	}
+
+	/*
+	 * Make sure page faults during pread are handled correctly.
+	 */
+	init('a', O_RDWR);
+	ret = do_read(fd, addr, page_size, page_size);
+	if (ret != page_size)
+		err(1, "pread %s: %ld != %u", filename, ret, page_size);
+	if (memcmp(addr, page, page_size))
+		errx(1, "pread is broken");
+	done();
+
+	init('b', O_RDWR | O_DIRECT);
+	ret = do_read(fd, addr, page_size, page_size);
+	if (ret != page_size)
+		err(1, "pread %s (O_DIRECT): %ld != %u", filename, ret, page_size);
+	if (memcmp(addr, page, page_size))
+		errx(1, "pread (D_DIRECT) is broken");
+	done();
+
+	/*
+	 * Make sure page faults during pwrite are handled correctly.
+	 */
+	init('c', O_RDWR);
+	ret = do_write(fd, addr + page_size, page_size, 0);
+	if (ret != page_size)
+		err(1, "pwrite %s: %ld != %u", filename, ret, page_size);
+	if (memcmp(addr, page, page_size))
+		errx(1, "pwrite is broken");
+	done();
+
+	init('d', O_RDWR | O_DIRECT);
+	ret = do_write(fd, addr + page_size, page_size, 0);
+	if (ret != page_size)
+		err(1, "pwrite %s (O_DIRECT): %ld != %u", filename, ret, page_size);
+	if (memcmp(addr, page, page_size))
+		errx(1, "pwrite (O_DIRECT) is broken");
+	done();
+
+	if (unlink(filename))
+		err(1, "unlink %s", filename);
+
+	return 0;
+}
diff --git a/tests/generic/639 b/tests/generic/639
new file mode 100755
index 00000000..4406be98
--- /dev/null
+++ b/tests/generic/639
@@ -0,0 +1,40 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Red Hat, Inc.  All Rights Reserved.
+#
+# FS QA Test 639
+#
+# Trigger mmap page faults in the same file during pread and pwrite
+#
+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 $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_require_test
+_require_test_program mmap-rw-fault
+
+$here/src/mmap-rw-fault $TEST_DIR/mmap-rw-fault.tmp 2>&1
+
+# success, all done
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/generic/639.out b/tests/generic/639.out
new file mode 100644
index 00000000..62c66537
--- /dev/null
+++ b/tests/generic/639.out
@@ -0,0 +1,2 @@
+QA output created by 639
+Silence is golden
diff --git a/tests/generic/group b/tests/generic/group
index 9a636b23..d6f11cda 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -641,3 +641,4 @@
 636 auto quick swap
 637 auto quick dir
 638 auto quick rw
+639 auto
-- 
2.26.3