generic/728: Add mmap + DIO write test

This is the same as generic/647, but with an additional test that writes
a memory-mapped page onto itself using direct I/O.

For direct I/O writes, the kernel will invalidate the page cache before
and after carrying out the write.  This puts filesystems that fault in
pages on demand and then carry out the write with page faults disabled
into a position in which they will not be able to make any progress.

src/mmap-rw-fault.c

@@ -20,6 +20,7 @@
 #include <string.h>
 #include <errno.h>
 #include <err.h>
+#include <getopt.h>
 
 char *filename;
 unsigned int page_size;
@@ -109,11 +110,29 @@ static ssize_t do_write(int fd, const void *buf, size_t count, off_t offset)
 	return count2;
 }
 
+static void usage(const char *argv0)
+{
+	fprintf(stderr, "Usage: %s [-2] {filename}\n", argv0);
+	exit(2);
+}
+
 int main(int argc, char *argv[])
 {
-	if (argc != 2)
-		errx(1, "no test filename argument given");
-	filename = argv[1];
+	int opt, opt_2 = 0;
+
+	while ((opt = getopt(argc, argv, "2")) != -1) {
+		switch(opt) {
+		case '2':
+			opt_2 = 1;
+			break;
+		default:
+			usage(argv[0]);
+		}
+	}
+
+	if (optind + 1 != argc)
+		usage(argv[0]);
+	filename = argv[optind];
 
 	page_size = ret = sysconf(_SC_PAGE_SIZE);
 	if (ret == -1)
@@ -179,6 +198,14 @@ int main(int argc, char *argv[])
 		errx(1, "pread (D_DIRECT) from hole is broken");
 	done();
 
+	if (opt_2) {
+		init('f', O_RDWR | O_DIRECT);
+		ret = do_write(fd, addr + page_size, page_size, page_size);
+		if (ret != page_size)
+			err(1, "pwrite %s (O_DIRECT): %ld != %u", filename, ret, page_size);
+		done();
+	}
+
 	if (unlink(filename))
 		err(1, "unlink %s", filename);
 

tests/generic/728

+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2023 Red Hat, Inc.  All Rights Reserved.
+#
+# FS QA Test 728
+#
+# Trigger page faults in the same file during read and write
+#
+# This is generic/647 with an additional test that writes a memory-mapped page
+# onto itself using direct I/O.
+#
+# The kernel will invalidate the page cache
+# before carrying out the write, so filesystems that fault in the target page before carrying out the direct I/O write will never make any progress.
+#
+. ./common/preamble
+_begin_fstest auto quick
+
+# Override the default cleanup function.
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	rm -f $TEST_DIR/mmap-rw-fault.tmp
+}
+
+# Import common functions.
+. ./common/filter
+
+# real QA test starts here
+
+_supported_fs generic
+_require_test
+_require_odirect
+_require_test_program mmap-rw-fault
+
+echo "Silence is golden"
+
+$here/src/mmap-rw-fault -2 $TEST_DIR/mmap-rw-fault.tmp
+
+status=$?
+exit

tests/generic/728.out

+QA output created by 728
+Silence is golden