zts: test syncfs() behaviour when pool suspends

Fairly coarse, but if it returns while the pool suspends, it must be
with an error.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Paul Dagnelie <paul.dagnelie@klarasystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Signed-off-by: Rob Norris <rob.norris@klarasystems.com>
Closes #17420

tests/runfiles/linux.run

@@ -210,6 +210,10 @@ tags = ['functional', 'simd']
 tests = ['snapshot_015_pos', 'snapshot_016_pos']
 tags = ['functional', 'snapshot']
 
+[tests/functional/syncfs:Linux]
+tests = ['syncfs_suspend']
+tags = ['functional', 'syncfs']
+
 [tests/functional/tmpfile:Linux]
 tests = ['tmpfile_001_pos', 'tmpfile_002_pos', 'tmpfile_003_pos',
     'tmpfile_stat_mode']

tests/zfs-tests/tests/Makefile.am

@@ -2064,6 +2064,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/stat/setup.ksh \
 	functional/stat/stat_001_pos.ksh \
 	functional/stat/statx_dioalign.ksh \
+	functional/syncfs/syncfs_suspend.ksh \
 	functional/suid/cleanup.ksh \
 	functional/suid/setup.ksh \
 	functional/suid/suid_write_to_none.ksh \

tests/zfs-tests/tests/functional/syncfs/syncfs_suspend.ksh

@@ -0,0 +1,115 @@
+#!/bin/ksh -p
+# SPDX-License-Identifier: CDDL-1.0
+#
+# CDDL HEADER START
+#
+# The contents of this file are subject to the terms of the
+# Common Development and Distribution License (the "License").
+# You may not use this file except in compliance with the License.
+#
+# You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+# or https://opensource.org/licenses/CDDL-1.0.
+# See the License for the specific language governing permissions
+# and limitations under the License.
+#
+# When distributing Covered Code, include this CDDL HEADER in each
+# file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+# If applicable, add the following below this CDDL HEADER, with the
+# fields enclosed by brackets "[]" replaced with your own identifying
+# information: Portions Copyright [yyyy] [name of copyright owner]
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2025, Klara, Inc.
+#
+
+. $STF_SUITE/include/libtest.shlib
+
+log_assert "syncfs() does not return success while the pool is suspended"
+
+typeset -i syncfs_pid=0
+
+function cleanup
+{
+	zinject -c all || true
+	zpool clear $TESTPOOL || true
+	test $syncfs_pid -gt 0 && kill -9 $syncfs_pid || true
+	destroy_pool $TESTPOOL
+}
+
+log_onexit cleanup
+
+DISK=${DISKS%% *}
+
+# create a single-disk pool, set failmode=wait
+log_must zpool create -o failmode=wait -f $TESTPOOL $DISK
+log_must zfs create -o recordsize=128k $TESTPOOL/$TESTFS
+
+# generate a write, then syncfs(), confirm success
+log_must touch /$TESTPOOL/$TESTFS/file1
+log_must sync -f /$TESTPOOL/$TESTFS
+
+# and again with no changes
+log_must sync -f /$TESTPOOL/$TESTFS
+
+# set up error injections to force the pool to suspend on next write
+log_must zinject -d $DISK -e io -T write $TESTPOOL
+log_must zinject -d $DISK -e nxio -T probe $TESTPOOL
+
+# generate another write
+log_must touch /$TESTPOOL/$TESTFS/file2
+
+# wait for the pool to suspend
+log_note "waiting for pool to suspend"
+typeset -i tries=10
+until [[ $(kstat_pool $TESTPOOL state) == "SUSPENDED" ]] ; do
+	if ((tries-- == 0)); then
+		log_fail "pool didn't suspend"
+	fi
+	sleep 1
+done
+
+# pool suspended. syncfs() in the background, as it may block
+sync -f /$TESTPOOL/$TESTFS &
+syncfs_pid=$!
+
+# give it a moment to get stuck
+sleep 1
+
+# depending on kernel version and pool config, syncfs should have either
+# returned an error, or be blocked in the kernel
+typeset -i blocked
+typeset -i rc
+if kill -0 $syncfs_pid ; then
+	blocked=1
+	log_note "syncfs() is blocked in the kernel"
+else
+	blocked=0
+	log_note "syncfs() returned while pool was suspended"
+
+	# exited, capture its error code directly
+	wait $syncfs_pid
+	rc=$?
+	syncfs_pid=0
+fi
+
+# bring the pool back online
+log_must zinject -c all
+log_must zpool clear $TESTPOOL
+
+if [[ $syncfs_pid -gt 0 ]] ; then
+	# it blocked, clean it up now
+	wait $syncfs_pid
+	rc=$?
+	syncfs_pid=0
+fi
+
+# if it returned when the pool was suspended, it must not claim success. if
+# it blocked and returned after the pool suspended, then we don't care about
+# the error (it depends on what happened after the pool resumed, which we're
+# not testing here)
+log_must test $blocked -eq 1 -o $rc -ne 0
+
+log_pass "syncfs() does not return success while the pool is suspended"