vdev probe to slow disk can stall mmp write checker

Simplify vdev probes in the zio_vdev_io_done context to
avoid holding the spa config lock for a long duration.

Also allow zpool clear if no evidence of another host
is using the pool.

Sponsored-by: Klara, Inc.
Sponsored-by: Wasabi Technology, Inc.
Reviewed-by: Olaf Faaland <faaland1@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <don.brady@klarasystems.com>
Closes #15839

tests/zfs-tests/tests/Makefile.am

@@ -1593,6 +1593,7 @@ nobase_dist_datadir_zfs_tests_tests_SCRIPTS += \
 	functional/mmp/mmp_on_zdb.ksh \
 	functional/mmp/mmp_reset_interval.ksh \
 	functional/mmp/mmp_write_distribution.ksh \
+	functional/mmp/mmp_write_slow_disk.ksh \
 	functional/mmp/mmp_write_uberblocks.ksh \
 	functional/mmp/multihost_history.ksh \
 	functional/mmp/setup.ksh \

tests/zfs-tests/tests/functional/mmp/mmp_write_slow_disk.ksh

@@ -0,0 +1,97 @@
+#!/bin/ksh -p
+#
+# CDDL HEADER START
+#
+# This file and its contents are supplied under the terms of the
+# Common Development and Distribution License ("CDDL"), version 1.0.
+# You may only use this file in accordance with the terms of version
+# 1.0 of the CDDL.
+#
+# A full copy of the text of the CDDL should have accompanied this
+# source.  A copy of the CDDL is also available via the Internet at
+# http://www.illumos.org/license/CDDL.
+#
+# CDDL HEADER END
+#
+
+#
+# Copyright (c) 2024, Klara Inc
+#
+
+# DESCRIPTION:
+#	Verify that long VDEV probes do not cause MMP checks to suspend pool
+#	Note: without PR-15839 fix, this test will suspend the pool.
+#
+#	A device that is returning unexpected errors will trigger a vdev_probe.
+#	When the device additionally has slow response times, the probe can hold
+#	the spa config lock as a writer for a long period of time such that the
+#	mmp uberblock updates stall when trying to acquire the spa config lock.
+#
+# STRATEGY:
+#	1. Create a pool with multiple leaf vdevs
+#	2. Enable multihost and multihost_history
+#	3. Delay for MMP writes to occur
+#	4. Verify that a long VDEV probe didn't cause MMP check to suspend pool
+#
+
+. $STF_SUITE/include/libtest.shlib
+. $STF_SUITE/tests/functional/mmp/mmp.cfg
+. $STF_SUITE/tests/functional/mmp/mmp.kshlib
+
+verify_runnable "both"
+
+function cleanup
+{
+	log_must zinject -c all
+
+	if [[ $(zpool list -H -o health $MMP_POOL) == "SUSPENDED" ]]; then
+		log_must zpool clear $MMP_POOL
+		zpool get state $MMP_POOL $MMP_DIR/file.3
+		zpool events | grep ".fs.zfs." | grep -v "history_event"
+	fi
+
+	poolexists $MMP_POOL && destroy_pool $MMP_POOL
+	log_must rm -r $MMP_DIR
+	log_must mmp_clear_hostid
+}
+
+log_assert "A long VDEV probe doesn't cause a MMP check suspend"
+log_onexit cleanup
+
+MMP_HISTORY_URL=/proc/spl/kstat/zfs/$MMP_POOL/multihost
+
+# Create a multiple drive pool
+log_must zpool events -c
+log_must mkdir -p $MMP_DIR
+log_must truncate -s 128M $MMP_DIR/file.{0,1,2,3,4,5}
+log_must zpool create -f $MMP_POOL \
+	mirror $MMP_DIR/file.{0,1,2} \
+	mirror $MMP_DIR/file.{3,4,5}
+
+# Enable MMP
+log_must mmp_set_hostid $HOSTID1
+log_must zpool set multihost=on $MMP_POOL
+clear_mmp_history
+
+# Inject vdev write error along with a delay
+log_must zinject -f 33 -e io -L pad2 -T write -d $MMP_DIR/file.3 $MMP_POOL
+log_must zinject -f 50 -e io -L uber -T write -d $MMP_DIR/file.3 $MMP_POOL
+log_must zinject -D 2000:4 -T write -d $MMP_DIR/file.3 $MMP_POOL
+
+log_must dd if=/dev/urandom of=/$MMP_POOL/data bs=1M count=5
+sleep 10
+sync_pool $MMP_POOL
+
+# Confirm mmp writes to the non-slow disks have taken place
+for x in {0,1,2,4}; do
+	write_count=$(grep -c file.${x} $MMP_HISTORY_URL)
+	[[ $write_count -gt 0 ]] || log_fail "expecting mmp writes"
+done
+
+# Expect that the pool was not suspended
+log_must check_state $MMP_POOL "" "ONLINE"
+health=$(zpool list -H -o health $MMP_POOL)
+log_note "$MMP_POOL health is $health"
+[[ "$health" == "SUSPENDED" ]] && log_fail "$MMP_POOL $health unexpected"
+
+log_pass "A long VDEV probe doesn't cause a MMP check suspend"