[PATCH v2] generic/637: Test page faults during pread and pwrite

[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          |   3 +-
 src/mmap-rw-fault.c   | 111 ++++++++++++++++++++++++++++++++++++++++++
 tests/generic/637     |  40 +++++++++++++++
 tests/generic/637.out |   2 +
 tests/generic/group   |   1 +
 5 files changed, 156 insertions(+), 1 deletion(-)
 create mode 100644 src/mmap-rw-fault.c
 create mode 100755 tests/generic/637
 create mode 100644 tests/generic/637.out

diff --git a/src/Makefile b/src/Makefile
index cc0b9579..13cdf19b 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -17,7 +17,8 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
 	t_mmap_cow_race t_mmap_fallocate fsync-err t_mmap_write_ro \
 	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_get_file_time t_create_short_dirs t_create_long_dirs t_enospc \
+	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..a652ac71
--- /dev/null
+++ b/src/mmap-rw-fault.c
@@ -0,0 +1,111 @@
+/* Trigger mmap page faults in the same file during pread and pwrite. */
+
+#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)
+{
+	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, O_RDWR);
+	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);
+}
+
+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('x');
+	ret = pread(fd, addr, page_size, page_size);
+	if (ret != page_size)
+		goto fail;
+	if (memcmp(addr, page, page_size))
+		errx(1, "pread is broken");
+	done();
+
+	/*
+	 * Make sure page faults during pwrite are handled correctly.
+	 */
+	init('y');
+	ret = pwrite(fd, addr + page_size, page_size, 0);
+	if (ret != page_size)
+		goto fail;
+	if (memcmp(addr, page, page_size))
+		errx(1, "pwrite is broken");
+	done();
+
+	if (unlink(filename))
+		goto fail;
+
+	return 0;
+
+fail:
+	err(1, "%s", filename);
+}
diff --git a/tests/generic/637 b/tests/generic/637
new file mode 100755
index 00000000..d3c3f235
--- /dev/null
+++ b/tests/generic/637
@@ -0,0 +1,40 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2021 Red Hat, Inc.  All Rights Reserved.
+#
+# FS QA Test 637
+#
+# 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 $tmp.*
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# real QA test starts here
+
+# Modify as appropriate.
+_supported_fs generic
+_require_test
+
+$here/src/mmap-rw-fault $TEST_DIR/mmap-rw-fault.tmp \
+|| exit
+
+# success, all done
+echo "Silence is golden"
+status=0
+exit
diff --git a/tests/generic/637.out b/tests/generic/637.out
new file mode 100644
index 00000000..55a3d825
--- /dev/null
+++ b/tests/generic/637.out
@@ -0,0 +1,2 @@
+QA output created by 637
+Silence is golden
diff --git a/tests/generic/group b/tests/generic/group
index 105763c4..01996b48 100644
--- a/tests/generic/group
+++ b/tests/generic/group
@@ -639,3 +639,4 @@
 634 auto quick atime bigtime
 635 auto quick atime bigtime shutdown
 636 auto quick swap
+637 auto
-- 
2.26.3