git: 2aca5deff7a0 - main - stress2: add a test for forced unmount racing mkdir at UFS_LINK_MAX

The branch main has been updated by sobomax:

URL: https://cgit.FreeBSD.org/src/commit/?id=2aca5deff7a0fb9f6f082d562f1ca85e707f674e

commit 2aca5deff7a0fb9f6f082d562f1ca85e707f674e
Author:     Maxim Sobolev <sobomax@FreeBSD.org>
AuthorDate: 2026-10-13 03:59:13 +0000
Commit:     Maxim Sobolev <sobomax@FreeBSD.org>
CommitDate: 2026-10-13 04:00:36 +0000

    stress2: add a test for forced unmount racing mkdir at UFS_LINK_MAX
    
    On a soft updates file system, keep a directory at UFS_LINK_MAX with
    workers removing and recreating subdirectories in it, so that mkdir(2)
    keeps going through ufs_sync_nlink(), and force-unmount, check and
    remount the file system in a loop.  The workers work relative to the
    directory: a lookup through the mount point would wait for the unmount
    on the covered vnode lock and never race with it.  Before the fix, the
    first forced unmount deadlocked with mkdir(2) sleeping in vfs_busy().
    
    With dtrace=1, count the vfs_busy() calls made during an unmount by
    caller, and the mkdir(2) calls that synced and restarted with ERELOOKUP
    during an unmount, which shows that the race was hit.
    
    Sponsored by:   Sippy Software, Inc.
    Reviewed by:    pho
    Tested by:      pho
    Differential Revision:  https://reviews.freebsd.org/D60204
    MFC after:      1 month
---
 tools/test/stress2/misc/nlink6.sh | 191 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 191 insertions(+)

diff --git a/tools/test/stress2/misc/nlink6.sh b/tools/test/stress2/misc/nlink6.sh
new file mode 100755
index 000000000000..6f9d2f4ca3a9
--- /dev/null
+++ b/tools/test/stress2/misc/nlink6.sh
@@ -0,0 +1,191 @@
+#!/bin/sh
+
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (c) 2026 Maksym Sobolyev <sobomax@FreeBSD.org>
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+# ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+# FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+# DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+# OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+# HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+# Forced unmount racing mkdir(2) in a directory at UFS_LINK_MAX on SU.
+#
+# With soft updates, rmdir(2) lowers the parent's i_effnlink at once and
+# its i_nlink only when the removal is on disk.  A mkdir(2) in between
+# finds i_nlink at UFS_LINK_MAX and goes through ufs_sync_nlink(), which
+# syncs the file system and restarts.  The sync used to busy the mount
+# and sleep in vfs_busy() while an unmount was in progress, with the
+# mkdir(2) still counted as a write by vn_start_write(), while the unmount
+# waited in vfs_write_suspend() for that write to end.  The unmount and
+# every later vfs_busy() of the mount point hung.
+#
+# Set dtrace=1 to count, while an unmount is in progress, the vfs_busy()
+# calls by caller, and the mkdir(2) calls that synced and restarted with
+# ERELOOKUP.  Without the fix, a vfs_busy() from ufs_sync_nlink() here is
+# the deadlock; with it, the mkdir(2) calls show the race was hit.
+
+[ `id -u` -ne 0 ] && echo "Must be root!" && exit 1
+
+. ../default.cfg
+
+UFS_LINK_MAX=`grep UFS_LINK_MAX /usr/include/ufs/ufs/dinode.h 2>/dev/null`
+[ -z "$UFS_LINK_MAX" ] && exit 0
+UFS_LINK_MAX=`echo $UFS_LINK_MAX | awk '{print $3}'`
+nworkers=8
+runtime=${runtime:-300}
+log=/tmp/nlink6.log
+
+cat > /tmp/nlink6.c <<EOF
+#include <sys/stat.h>
+#include <ufs/ufs/dinode.h>
+#include <err.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <time.h>
+#include <unistd.h>
+
+/*
+ * "setup": fill directory d with subdirectories up to UFS_LINK_MAX, the
+ * first nworkers of them named w<id>.
+ * "work <d> <id> <seconds>": remove and recreate <d>/w<id> in a loop.
+ * Work relative to <d>: a lookup through the mount point would wait for
+ * the unmount on the covered vnode lock and never race with it.
+ */
+int
+main(int argc, char *argv[])
+{
+	char path[1024];
+	time_t start;
+	int i, nworkers, secs;
+
+	if (argc == 3 && strcmp(argv[1], "setup") == 0) {
+		nworkers = atoi(argv[2]);
+		if (mkdir("d", 0755) == -1)
+			err(1, "mkdir(d)");
+		for (i = 0; i < UFS_LINK_MAX - 2; i++) {
+			if (i < nworkers)
+				snprintf(path, sizeof(path), "d/w%d", i);
+			else
+				snprintf(path, sizeof(path), "d/%d", i);
+			if (mkdir(path, 0755) == -1)
+				err(1, "mkdir(%s)", path);
+		}
+		return (0);
+	}
+	if (argc != 5 || strcmp(argv[1], "work") != 0)
+		errx(1, "usage: nlink6 setup <n> | work <dir> <id> <seconds>");
+	if (chdir(argv[2]) == -1)
+		err(1, "chdir(%s)", argv[2]);
+	snprintf(path, sizeof(path), "w%s", argv[3]);
+	secs = atoi(argv[4]);
+	start = time(NULL);
+	while (time(NULL) - start < secs) {
+		/* Errors are expected once the file system is gone. */
+		if (rmdir(path) == -1 || mkdir(path, 0755) == -1)
+			usleep(1000);
+	}
+	return (0);
+}
+EOF
+mycc -o /tmp/nlink6 -Wall -Wextra -O2 /tmp/nlink6.c || exit 1
+rm /tmp/nlink6.c
+
+set -e
+mount | grep -q "on $mntpoint " && umount -f $mntpoint
+mdconfig -l | grep -q "md$mdstart" && mdconfig -d -u $mdstart
+mdconfig -a -t swap -s 1g -u $mdstart
+newfs -Un /dev/md$mdstart > /dev/null
+mount /dev/md$mdstart $mntpoint
+(cd $mntpoint; /tmp/nlink6 setup $nworkers)
+umount $mntpoint
+set +e
+
+if [ "$dtrace" = 1 ]; then
+	# The unmount-in-progress flag (MNTK_UNMOUNT) is 0x01000000.
+	dtrace -q -n 'fbt::vfs_busy:entry
+	    /(args[0]->mnt_kern_flag & 0x01000000) != 0/
+	    { @b[stack(2)] = count(); }
+	fbt::ufs_mkdir:entry { self->mp = args[0]->a_dvp->v_mount; }
+	fbt::ufs_mkdir:return
+	    /self->mp != NULL && (int)arg1 == -5 &&
+	    (self->mp->mnt_kern_flag & 0x01000000) != 0/
+	    { @m = count(); }
+	fbt::ufs_mkdir:return { self->mp = NULL; }
+	END {
+		printf("vfs_busy() during unmount, by caller:");
+		printa(@b);
+		printa("mkdir(2) synced and restarted during unmount: %@d\n",
+		    @m);
+	}' > $log.dtrace &
+	dpid=$!
+	sleep 5
+fi
+
+s=0
+start=`date +%s`
+n=0
+while [ $((`date +%s` - start)) -lt $runtime ]; do
+	mount /dev/md$mdstart $mntpoint || { s=1; break; }
+	pids=
+	for i in `jot $nworkers 0`; do
+		/tmp/nlink6 work $mntpoint/d $i 10 &
+		pids="$pids $!"
+	done
+	sleep `jot -r 1 1 5`
+	umount -f $mntpoint &
+	upid=$!
+	t=0
+	while kill -0 $upid 2>/dev/null; do
+		sleep 1
+		t=$((t + 1))
+		if [ $t -eq 120 ]; then
+			echo "FAIL: umount -f $mntpoint is stuck"
+			procstat -kk $upid `pgrep -x nlink6`
+			if [ -n "$dpid" ]; then
+				kill -TERM $dpid
+				wait $dpid
+				cat $log.dtrace
+			fi
+			# The mount point stays busy, leave everything as is.
+			exit 1
+		fi
+	done
+	wait $upid $pids
+	n=$((n + 1))
+	if ! fsck_ffs -fy /dev/md$mdstart > $log 2>&1; then
+		echo "FAIL: fsck_ffs exit $? after cycle $n"
+		tail -20 $log
+		s=1
+		break
+	fi
+done
+echo "$n forced unmounts"
+
+if [ -n "$dpid" ]; then
+	kill -TERM $dpid
+	wait $dpid
+	cat $log.dtrace
+fi
+mdconfig -d -u $mdstart
+rm -f /tmp/nlink6 $log $log.dtrace
+exit $s