generic: concurrent non-overlapping direct I/O on the same extents

There have been a couple of logic bugs in `btrfs_get_extent()` which
could lead to spurious -EEXIST errors from read or write. This test
exercises those conditions by having two threads race to add an
extent to the extent map.

This is fixed by Linux commit 8dff9c853410 ("Btrfs: deal with
duplciates during extent_map insertion in btrfs_get_extent") and the
patch "Btrfs: deal with existing encompassing extent map in
btrfs_get_extent()"
(http://marc.info/?l=linux-btrfs&m=147873402311143&w=2).

Although the bug is Btrfs-specific, nothing about the test is.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>

.gitignore

@@ -44,6 +44,7 @@
 /src/bulkstat_unlink_test_modified
 /src/dbtest
 /src/devzero
+/src/dio-interleaved
 /src/dirperf
 /src/dirstress
 /src/dmiperf

src/Makefile

@@ -21,7 +21,7 @@ LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
 	stale_handle pwrite_mmap_blocked t_dir_offset2 seek_sanity_test \
 	seek_copy_test t_readdir_1 t_readdir_2 fsync-tester nsexec cloner \
 	renameat2 t_getcwd e4compact test-nextquota punch-alternating \
-	attr-list-by-handle-cursor-test listxattr
+	attr-list-by-handle-cursor-test listxattr dio-interleaved
 
 SUBDIRS =
 

src/dio-interleaved.c

@@ -0,0 +1,98 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+#include <errno.h>
+#include <fcntl.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+
+static pthread_barrier_t barrier;
+
+static unsigned long extent_size;
+static unsigned long num_extents;
+
+struct dio_thread_data {
+	int fd;
+	int thread_id;
+};
+
+static void *dio_thread(void *arg)
+{
+	struct dio_thread_data *data = arg;
+	off_t off;
+	ssize_t ret;
+	void *buf;
+
+	if ((errno = posix_memalign(&buf, extent_size / 2, extent_size / 2))) {
+		perror("malloc");
+		return NULL;
+	}
+	memset(buf, 0, extent_size / 2);
+
+	off = (num_extents - 1) * extent_size;
+	if (data->thread_id)
+		off += extent_size / 2;
+	while (off >= 0) {
+		pthread_barrier_wait(&barrier);
+
+		ret = pread(data->fd, buf, extent_size / 2, off);
+		if (ret == -1)
+			perror("pread");
+
+		off -= extent_size;
+	}
+
+	free(buf);
+	return NULL;
+}
+
+int main(int argc, char **argv)
+{
+	struct dio_thread_data data[2];
+	pthread_t thread;
+	int fd;
+
+	if (argc != 4) {
+		fprintf(stderr, "usage: %s EXTENT_SIZE NUM_EXTENTS PATH\n",
+			argv[0]);
+		return EXIT_FAILURE;
+	}
+
+	extent_size = strtoul(argv[1], NULL, 0);
+	num_extents = strtoul(argv[2], NULL, 0);
+
+	errno = pthread_barrier_init(&barrier, NULL, 2);
+	if (errno) {
+		perror("pthread_barrier_init");
+		return EXIT_FAILURE;
+	}
+
+	fd = open(argv[3], O_RDONLY | O_DIRECT);
+	if (fd == -1) {
+		perror("open");
+		return EXIT_FAILURE;
+	}
+
+	data[0].fd = fd;
+	data[0].thread_id = 0;
+	errno = pthread_create(&thread, NULL, dio_thread, &data[0]);
+	if (errno) {
+		perror("pthread_create");
+		close(fd);
+		return EXIT_FAILURE;
+	}
+
+	data[1].fd = fd;
+	data[1].thread_id = 1;
+	dio_thread(&data[1]);
+
+	pthread_join(thread, NULL);
+
+	close(fd);
+	return EXIT_SUCCESS;
+}

tests/generic/391

@@ -0,0 +1,76 @@
+#! /bin/bash
+# FS QA Test 391
+#
+# Test two threads doing non-overlapping direct I/O in the same extents.
+# Motivated by a bug in Btrfs' direct I/O get_block function which would lead
+# to spurious -EEXIST failures from direct I/O reads.
+#
+#-----------------------------------------------------------------------
+# Copyright (c) 2016 Facebook.  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/$$
+status=1	# failure is the default!
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+_cleanup()
+{
+	cd /
+	rm -f $tmp.*
+	rm -f "$testfile"
+}
+
+# get standard environment, filters and checks
+. ./common/rc
+. ./common/filter
+
+# remove previous $seqres.full before test
+rm -f $seqres.full
+
+# real QA test starts here
+
+_supported_fs generic
+_supported_os Linux
+_require_test
+_require_xfs_io_command "falloc"
+_require_test_program "dio-interleaved"
+
+extent_size="$(($(get_block_size "$TEST_DIR") * 2))"
+num_extents=1024
+testfile="$TEST_DIR/$$-testfile"
+
+$XFS_IO_PROG -fc "truncate 0" "$testfile"
+for ((off = 0; off < num_extents * extent_size; off += extent_size)); do
+	$XFS_IO_PROG -c "falloc $off $extent_size" "$testfile"
+done
+
+# To reproduce the Btrfs bug, the extent map must not be cached in memory.
+sync
+echo 3 > /proc/sys/vm/drop_caches
+
+"$here/src/dio-interleaved" "$extent_size" "$num_extents" "$testfile"
+
+echo "Silence is golden"
+
+# success, all done
+status=0
+exit

tests/generic/391.out

@@ -0,0 +1,2 @@
+QA output created by 391
+Silence is golden

tests/generic/group

@@ -393,3 +393,4 @@
 388 auto log metadata
 389 auto quick acl
 390 auto freeze stress dangerous
+391 auto quick rw