generic: add a regression test for fiemap into an mmap range

Btrfs had a deadlock that you could trigger by mmap'ing a large file and
using that as the buffer for fiemap.  This test adds a c program to do
this, and the fstest creates a large enough file and then runs the
reproducer on the file.  Without the fix btrfs deadlocks, with the fix
we pass fine.

Signed-off-by: Josef Bacik <[email protected]>
Reviewed-by: Anand Jain <[email protected]>
Reviewed-by: Filipe Manana <[email protected]>
Reviewed-by: "Darrick J. Wong" <[email protected]>
Reviewed-by: Zorro Lang <[email protected]>
Signed-off-by: Zorro Lang <[email protected]>

.gitignore

@@ -205,6 +205,7 @@ tags
 /src/vfs/mount-idmapped
 /src/log-writes/replay-log
 /src/perf/*.pyc
+/src/fiemap-fault
 
 # Symlinked files
 /tests/generic/035.out

src/Makefile

@@ -34,7 +34,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	attr_replace_test swapon mkswap t_attr_corruption t_open_tmpfiles \
 	fscrypt-crypt-util bulkstat_null_ocount splice-test chprojid_fail \
 	detached_mounts_propagation ext4_resize t_readdir_3 splice2pipe \
-	uuid_ioctl t_snapshot_deleted_subvolume
+	uuid_ioctl t_snapshot_deleted_subvolume fiemap-fault
 
 EXTRA_EXECS = dmerror fill2attr fill2fs fill2fs_check scaleread.sh \
 	      btrfs_crc32c_forged_name.py popdir.pl popattr.py \

src/fiemap-fault.c

@@ -0,0 +1,74 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
+ */
+
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <linux/fs.h>
+#include <linux/types.h>
+#include <linux/fiemap.h>
+#include <err.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+
+int prep_mmap_buffer(int fd, void **addr)
+{
+	struct stat st;
+	int ret;
+
+	ret = fstat(fd, &st);
+	if (ret)
+		err(1, "failed to stat %d", fd);
+
+	*addr = mmap(NULL, st.st_size, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0);
+	if (*addr == MAP_FAILED)
+		err(1, "failed to mmap %d", fd);
+
+	return st.st_size;
+}
+
+int main(int argc, char *argv[])
+{
+	struct fiemap *fiemap;
+	size_t sz, last = 0;
+	void *buf = NULL;
+	int ret, fd;
+
+	if (argc != 2)
+		errx(1, "no in and out file name arguments given");
+
+	fd = open(argv[1], O_RDWR, 0666);
+	if (fd == -1)
+		err(1, "failed to open %s", argv[1]);
+
+	sz = prep_mmap_buffer(fd, &buf);
+
+	fiemap = (struct fiemap *)buf;
+	fiemap->fm_flags = 0;
+	fiemap->fm_extent_count = (sz - sizeof(struct fiemap)) /
+				  sizeof(struct fiemap_extent);
+
+	while (last < sz) {
+		int i;
+
+		fiemap->fm_start = last;
+		fiemap->fm_length = sz - last;
+
+		ret = ioctl(fd, FS_IOC_FIEMAP, (unsigned long)fiemap);
+		if (ret < 0)
+			err(1, "fiemap failed %d", errno);
+		for (i = 0; i < fiemap->fm_mapped_extents; i++)
+		       last = fiemap->fm_extents[i].fe_logical +
+			       fiemap->fm_extents[i].fe_length;
+	}
+
+	munmap(buf, sz);
+	close(fd);
+	return 0;
+}

tests/generic/742

@@ -0,0 +1,50 @@
+#! /bin/bash
+# SPDX-License-Identifier: GPL-2.0
+# Copyright (c) 2024 Meta Platforms, Inc.  All Rights Reserved.
+#
+# FS QA Test No. 742
+#
+# Test fiemap into an mmaped buffer of the same file
+#
+# Create a reasonably large file, then run a program which mmaps it and uses
+# that as a buffer for an fiemap call.  This is a regression test for btrfs
+# where we used to hold a lock for the duration of the fiemap call which would
+# result in a deadlock if we page faulted.
+#
+. ./common/preamble
+_begin_fstest quick auto fiemap
+[ $FSTYP == "btrfs" ] && \
+	_fixed_by_kernel_commit b0ad381fa769 \
+		"btrfs: fix deadlock with fiemap and extent locking"
+
+_cleanup()
+{
+	rm -f $dst
+	cd /
+	rm -r -f $tmp.*
+}
+
+# real QA test starts here
+_supported_fs generic
+_require_test
+_require_test_program "fiemap-fault"
+_require_test_program "punch-alternating"
+_require_xfs_io_command "fpunch"
+
+dst=$TEST_DIR/$seq/fiemap-fault
+
+mkdir -p $TEST_DIR/$seq
+
+echo "Silence is golden"
+
+# Generate a file with lots of extents
+blksz=$(_get_file_block_size $TEST_DIR)
+$XFS_IO_PROG -f -c "pwrite -q 0 $((blksz * 10000))" $dst
+$here/src/punch-alternating $dst
+
+# Now run the reproducer
+$here/src/fiemap-fault $dst
+
+# success, all done
+status=$?
+exit

tests/generic/742.out

@@ -0,0 +1,2 @@
+QA output created by 742
+Silence is golden